saving Panel with PeriodIndex to HDF in table format loses Period information
```
(Pdb) print pd.__version__
0.14.0-403-ge131df1
(Pdb) print data
<class 'pandas.core.panel.Panel'>
Dimensions: 2 (items) x 35 (major_axis) x 21 (minor_axis)
Items axis: Constant Prices to Current Prices
Major_axis axis: Andaman & Nicobar to West Bengal
Minor_axis axis: 1994 to 2014
(Pdb) print data.minor_axis
<class 'pandas.tseries.period.PeriodIndex'>
[1994, ..., 2014]
Length: 21, Freq: A-MAR
(Pdb) data.to_hdf("test.h5", "test_no_table")
(Pdb) data.to_hdf("test.h5", "test_table", format="table")
(Pdb) pd.read_hdf("test.h5", "/test_no_table").minor_axis
<class 'pandas.tseries.period.PeriodIndex'>
[1994, ..., 2014]
Length: 21, Freq: A-MAR
(Pdb) pd.read_hdf("test.h5", "/test_table").minor_axis
Int64Index([35, 36, 37, 38, 39, 40, 41, 42, 43, 44], dtype='int64')
```
