ENH: Declare a BoolBlock as a NumericBlock
BUG: GH2641 fixes "df.decribe() with boolean column"

This change will make all numeric operations on boolean data work, by
just transparently treating them as integers values 1 and 0.  This is
not pandas specific behavior, this is the default operations of both
numpy and python.
Merge pull request #3162 from danbirken/bool_as_numeric_type

ENH: Declare a BoolBlock as a NumericBlock