BUG Deprecating use of bool() on DataFrame, GH #1069
Calling bool() on DataFrame raises issues described in #1069. This
change causes DataFrame to raise a ValueError when called with bool(),
and instead provides a new property, dataframe.empty.

This will cause client code to break, but I think it will prevent more bugs in the long run. I'll include it in the upcoming 0.8.0 (May, sometime)
