BUG: loffset isn't applied when using resample() with a TimedeltaIndex
#### Code Sample, a copy-pastable example if possible

```
In [3]: from pandas import *
In [4]: rng = timedelta_range(start='0s', periods=10, freq='s')
In [5]: df = DataFrame({'A' : range(10)}, index=rng)
In [6]: df.resample('2S', loffset='2h').count()
Out[6]: 
          A
00:00:00  2
00:00:02  2
00:00:04  2
00:00:06  2
00:00:08  2

```
#### Expected Output

```
          A
02:00:00  2
02:00:02  2
02:00:04  2
02:00:06  2
02:00:08  2
```
#### output of `pd.show_versions()`

```
INSTALLED VERSIONS
------------------
commit: cff1f5595888becee0e58dedf014a12e8131b352
python: 3.5.2.final.0
python-bits: 64
OS: Linux
OS-release: 4.4.0-21-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: en_US.UTF-8

pandas: 0.18.1+327.gcff1f55
nose: 1.3.7
pip: 8.1.2
setuptools: 23.0.0
Cython: 0.24.1
numpy: 1.11.1
scipy: 0.18.0
statsmodels: None
xarray: None
IPython: 4.2.0
sphinx: None
patsy: None
dateutil: 2.5.3
pytz: 2016.6.1
blosc: None
bottleneck: None
tables: 3.2.3.1
numexpr: 2.6.1
matplotlib: None
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: None
httplib2: None
apiclient: None
sqlalchemy: None
pymysql: None
psycopg2: None
jinja2: None
boto: None
pandas_datareader: None
```

I'm working on #13218 and can't proceed with writing the tests due to this bug. I will try to see if I can fix it, but I'm not totally sure if I will be able to.
