Cannot append DataFrames with uint dtypes to HDFStore
Trying to store DataFrames with unsigned integer dtypes in HDFStore fails due to a bug in the `get_atom_data` methods of the `DataCol` and `DataIndexableCol` classes in `pandas.io.pytables`.  These methods use Python's `capitalize` method to map dtypes to PyTables column types, and fail because PyTables' unsigned int classes start with two capital letters (e.g., UInt32Col).  This error occurs on 0.11 and the current master:

``` python
import pandas as pd
import numpy as np

uint8_series = pd.Series(np.random.random_integers(0,high=255,size=5), dtype=np.uint8)
udf = pd.DataFrame({'u08': uint8_series}, index=np.arange(5))

store = pd.HDFStore('uint.h5')

# this invocation will throw an error in pandas 0.11 and current master
store.append('uints', udf)
```

I have a commit + test on my fork that fixes this, just needed to submit the bug here first to have the right commit message on my fork, per contribution standards.  First time committer.
