ENH: HDFStore enhancements
- will retain index attributes (freq,tz,name) on recreation #3499
- support datelike columns with a timezone as data_columns #2852
- will raise if trying to append with a different timezone than existing

will warn if the existing frequency of an index is different than an appended one
(thought raising was too strict)

```
In [5]: df  = DataFrame(dict(A = Series(xrange(3), index=date_range('2000-1-1',periods=3,freq='H'))))

In [6]: df2 = DataFrame(dict(A = Series(xrange(3), index=date_range('2002-1-1',periods=3,freq='D'))))

In [9]: df.index
Out[9]: 
<class 'pandas.tseries.index.DatetimeIndex'>
[2000-01-01 00:00:00, ..., 2000-01-01 02:00:00]
Length: 3, Freq: H, Timezone: None

In [10]: df2.index
Out[10]: 
<class 'pandas.tseries.index.DatetimeIndex'>
[2002-01-01 00:00:00, ..., 2002-01-03 00:00:00]
Length: 3, Freq: D, Timezone: None

In [12]: df.to_hdf('test.h5','data',mode='w',append=True)

In [13]: df2.to_hdf('test.h5','data',append=True)
pandas/io/pytables.py:1148: FrequencyWarning: 
the frequency of the existing index is [<1 Hour>] which conflicts with the new freq [<1 Day>],
resetting the frequency to None

  warnings.warn(ws, FrequencyWarning)

```
