Cannot add TimedeltaIndex to tz-aware DatetimeIndex (but can to non-tz-aware DatetimeIndex)
#### Code Sample, a copy-pastable example if possible

Under 0.19.1 and latest master:

```python
In [19]: dr = pd.date_range("20161123 00:00", "20161123 02:00", freq="H")                           
                                                                                                    
In [20]: tdr = pd.timedelta_range("1 minute", "3 minutes", freq="T")                                
                                                                                                    
In [21]: dr + tdr                                                                                   
Out[21]:                                                                                            
DatetimeIndex(['2016-11-23 00:01:00', '2016-11-23 01:02:00',                                        
               '2016-11-23 02:03:00'],                                                              
              dtype='datetime64[ns]', freq='61T')                                                   
                                                                                                    
In [22]: dr_tz = pd.date_range("20161123 00:00", "20161123 02:00", freq="H", tz="America/New_York") 
    ...:                                                                                            
                                                                                                    
In [23]: dr_tz + tdr                                                                                
---------------------------------------------------------------------------                         
TypeError                                 Traceback (most recent call last)                         
<ipython-input-23-c10d4a537816> in <module>()                                                       
----> 1 dr_tz + tdr                                                                                 
                                                                                                    
C:\Anaconda\envs\bleeding\lib\site-packages\pandas\tseries\base.pyc in __add__(self, other)         
    617             from pandas.tseries.offsets import DateOffset                                   
    618             if isinstance(other, TimedeltaIndex):                                           
--> 619                 return self._add_delta(other)                                               
    620             elif isinstance(self, TimedeltaIndex) and isinstance(other, Index):             
    621                 if hasattr(other, '_add_delta'):                                            
                                                                                                    
C:\Anaconda\envs\bleeding\lib\site-packages\pandas\tseries\index.pyc in _add_delta(self, delta)     
    787             new_values = self._add_delta_td(delta)                                          
    788         elif isinstance(delta, TimedeltaIndex):                                             
--> 789             new_values = self._add_delta_tdi(delta)                                         
    790             # update name when delta is Index                                               
    791             name = com._maybe_match_name(self, delta)                                       
                                                                                                    
C:\Anaconda\envs\bleeding\lib\site-packages\pandas\tseries\base.pyc in _add_delta_tdi(self, other)  
    704             mask = (self._isnan) | (other._isnan)                                           
    705             new_values[mask] = tslib.iNaT                                                   
--> 706         return new_values.view(self.dtype)                                                  
    707                                                                                             
    708     def isin(self, values):                                                                 
                                                                                                    
TypeError: data type not understood                             

```

#### Problem description
Given a DatetimeIndex that is not tz-aware, adding a TimedeltaIndex of the same length adds the values elementwise, as one would expect. Given a tz-aware DatetimeIndex, however, adding a TimedeltaIndex results in TypeError. Performing the same operation by iterating over the tz-aware index and adding the values directly works in the expected manner. This behavior did not occur under pandas 0.16.2; however, the above behavior occurs under at least 0.19.1 and the latest master.

#### Expected Output
Equivalent to the elementwise operation below, which works on latest master:
```python
In [25]: pd.Index([dr_tz[i] + tdr[i] for i in xrange(len(dr_tz))])                                  
Out[25]:                                                                                            
DatetimeIndex(['2016-11-23 00:01:00-05:00', '2016-11-23 01:02:00-05:00',                            
               '2016-11-23 02:03:00-05:00'],                                                        
              dtype='datetime64[ns, America/New_York]', freq=None)                                  
```

This also worked under 0.16.2:
```python
In [14]: dr_tz = pd.date_range("20161123 00:00", "20161123 02:00", freq="H", tz="America/New_York") 
                                                                                                    
In [15]: tdr = pd.timedelta_range("1 minute", "3 minutes", freq="T")                                
                                                                                                    
In [16]: dr_tz + tdr                                                                                
Out[16]:                                                                                            
DatetimeIndex(['2016-11-23 00:01:00-05:00', '2016-11-23 01:02:00-05:00',                            
               '2016-11-23 02:03:00-05:00'],                                                        
              dtype='datetime64[ns]', freq='61T', tz='America/New_York')     
```


#### Output of ``pd.show_versions()``

<details>
In [26]: pd.show_versions()                                                                         
                                                                                                    
INSTALLED VERSIONS                                                                                  
------------------                                                                                  
commit: None                                                                                        
python: 2.7.12.final.0                                                                              
python-bits: 64                                                                                     
OS: Windows                                                                                         
OS-release: 7                                                                                       
machine: AMD64                                                                                      
processor: Intel64 Family 6 Model 62 Stepping 4, GenuineIntel                                       
byteorder: little                                                                                   
LC_ALL: None                                                                                        
LANG: None                                                                                          
LOCALE: None.None                                                                                   
                                                                                                    
pandas: 0.19.0+98.gc045e1d                                                                          
nose: 1.3.7                                                                                         
pip: 9.0.1                                                                                          
setuptools: 27.2.0                                                                                  
Cython: 0.24.1                                                                                      
numpy: 1.11.2                                                                                       
scipy: 0.18.1                                                                                       
statsmodels: None                                                                                   
xarray: None                                                                                        
IPython: 5.1.0                                                                                      
sphinx: 1.4.8                                                                                       
patsy: None                                                                                         
dateutil: 2.5.3                                                                                     
pytz: 2016.7                                                                                        
blosc: None                                                                                         
bottleneck: None                                                                                    
tables: 3.2.2                                                                                       
numexpr: 2.6.1                                                                                      
matplotlib: 1.5.3                                                                                   
openpyxl: 2.4.0                                                                                     
xlrd: 1.0.0                                                                                         
xlwt: 1.1.2                                                                                         
xlsxwriter: None                                                                                    
lxml: 3.6.4                                                                                         
bs4: None                                                                                           
html5lib: None                                                                                      
httplib2: None                                                                                      
apiclient: None                                                                                     
sqlalchemy: 1.0.13                                                                                  
pymysql: None                                                                                       
psycopg2: None                                                                                      
jinja2: 2.8                                                                                         
boto: None                                                                                          
pandas_datareader: None                  
</details>
