[BUG] deepcopy corrupts block manager

[Sabri Eyuboglu]

A call to copy.deepcopy on a datapanel corrupts _block_index of the columns:

dp = mk.DataPanel({
    "a": pd.Series([0,1,2,3]),
    "b": pd.Series([0,1,2,3]),
    "c": pd.Series([0,1,2,3]),
})
dp.consolidate()
print(dp["a"]._block_index)

import copy

dp = copy.deepcopy(dp)
print(dp["a"]._block_index)