DatetimeIndex.to_series loses timezone information
``` python
>> f
<class 'pandas.tseries.index.DatetimeIndex'>
[2014-07-25 07:00:37+00:00, ..., 2014-07-26 07:50:17+00:00]
Length: 53304, Freq: None, Timezone: UTC
>> f.to_series()
datetime
2014-07-25 07:00:37+00:00   2014-07-25 07:00:37
2014-07-25 07:11:36+00:00   2014-07-25 07:11:36
2014-07-25 08:01:48+00:00   2014-07-25 08:01:48
2014-07-23 07:00:31+00:00   2014-07-23 07:00:31
2014-07-23 07:00:40+00:00   2014-07-23 07:00:40
2014-07-23 17:27:36+00:00   2014-07-23 17:27:36
2014-07-23 17:33:00+00:00   2014-07-23 17:33:00
2014-07-23 19:44:10+00:00   2014-07-23 19:44:10
2014-07-23 20:10:50+00:00   2014-07-23 20:10:50
2014-07-21 07:10:18+00:00   2014-07-21 07:10:18
2014-07-21 07:49:06+00:00   2014-07-21 07:49:06
2014-07-21 21:54:48+00:00   2014-07-21 21:54:48
2014-07-25 07:00:23+00:00   2014-07-25 07:00:23
2014-07-25 07:00:23+00:00   2014-07-25 07:00:23
2014-07-25 08:06:16+00:00   2014-07-25 08:06:16
...
2014-07-27 19:49:12+00:00   2014-07-27 19:49:12
2014-07-27 19:49:28+00:00   2014-07-27 19:49:28
2014-07-27 19:50:10+00:00   2014-07-27 19:50:10
2014-07-27 19:51:51+00:00   2014-07-27 19:51:51
2014-07-27 19:51:52+00:00   2014-07-27 19:51:52
2014-07-27 19:52:52+00:00   2014-07-27 19:52:52
2014-07-26 12:52:46+00:00   2014-07-26 12:52:46
2014-07-26 12:52:46+00:00   2014-07-26 12:52:46
2014-07-26 12:52:46+00:00   2014-07-26 12:52:46
2014-07-23 16:04:22+00:00   2014-07-23 16:04:22
2014-07-23 16:04:22+00:00   2014-07-23 16:04:22
2014-07-23 16:04:22+00:00   2014-07-23 16:04:22
2014-07-26 07:50:07+00:00   2014-07-26 07:50:07
2014-07-26 07:50:16+00:00   2014-07-26 07:50:16
2014-07-26 07:50:17+00:00   2014-07-26 07:50:17
Name: datetime, Length: 53304
>> pd.show_versions()
INSTALLED VERSIONS
------------------
commit: None
python: 2.7.7.final.0
python-bits: 64
OS: Windows
OS-release: 8
machine: AMD64
processor: Intel64 Family 6 Model 42 Stepping 7, GenuineIntel
byteorder: little
LC_ALL: None
LANG: None

pandas: 0.14.0
nose: 1.3.3
Cython: 0.20.1
numpy: 1.8.1
scipy: 0.14.0
statsmodels: 0.5.0
IPython: 2.1.0
sphinx: 1.2.2
patsy: 0.2.1
scikits.timeseries: None
dateutil: 1.5
pytz: 2014.3
bottleneck: None
tables: 3.1.1
numexpr: 2.3.1
matplotlib: 1.3.1
openpyxl: 1.8.5
xlrd: 0.9.3
xlwt: 0.7.5
xlsxwriter: 0.5.5
lxml: 3.3.5
bs4: 4.3.1
html5lib: None
bq: None
apiclient: None
rpy2: None
sqlalchemy: 0.9.4
pymysql: None
psycopg2: None
```
