pandas.tslib.normalize_date()  can put Timestamp into inconsistent state
### Code and Error description

If I try to normalize a date on daylight saving date day, the normalize_date() can put a Timestamp object into inconsistent state.

``` python
>>> import pandas as pd
>>> original_midnight = pd.Timestamp('20121104', tz='US/Eastern')
>>> original_midday = pd.Timestamp('20121104T120000', tz='US/Eastern')

>>> str(pd.tslib.normalize_date(original_midday))
'2012-11-04 00:00:00-05:00'

>>> str(original_midnight)
'2012-11-04 00:00:00-04:00'

>>> pd.tslib.normalize_date(original_midday) == original_midnight
False

>>> pd.tslib.normalize_date(original_midday).tzinfo
<DstTzInfo 'US/Eastern' EST-1 day, 19:00:00 STD>
>>> original_midnight.tzinfo
<DstTzInfo 'US/Eastern' EDT-1 day, 20:00:00 DST>
```

according to the [implementation](https://github.com/pydata/pandas/blob/master/pandas/tslib.pyx#L4303-L4317) It only replaces the with zeroes the time part.

I believe either the replace should be timezone aware or the function should look like this:

``` python
if PyDateTime_Check(dt):
    return pd.Timestamp(dt.date(), tz=dt.tz)
elif PyDate_Check(dt):
    return datetime(dt.year, dt.month, dt.day)
else:
    raise TypeError('Unrecognized type: %s' % type(dt))
```
#### INSTALLED VERSIONS

---

commit: None
python: 2.7.6.final.0
python-bits: 64
OS: Linux
OS-release: 3.16.0-44-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8

pandas: 0.16.2
nose: 1.3.0
Cython: 0.22.1
numpy: 1.9.2
scipy: 0.15.1
statsmodels: 0.6.1
IPython: 3.2.0
sphinx: None
patsy: 0.2.1
dateutil: 2.4.2
pytz: 2015.4
bottleneck: 0.8.0
tables: 3.0.0
numexpr: 2.3
matplotlib: 1.4.3
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: None
httplib2: None
apiclient: None
sqlalchemy: None
pymysql: None
psycopg2: None
