Possible bug with  BMonthEnd()
> > > import pandas
> > > from pandas.tseries.offsets import *
> > > import datetime as dt
> > > d = dt.datetime(2013, 6, 28, 0, 0)
> > > d + BMonthEnd()
> > > datetime.datetime(2013, 7, 31, 0, 0)
> > > d = dt.datetime(2013, 6, 28, 12, 0)
> > > d + BMonthEnd()
> > > datetime.datetime(2013, 7, 31, 0, 0)

At noon on 6/28 end of business month is 23:59, not the start of the 
day... Bug, I think????
