Weekly anchored frequency offsets don't behave as expected
For example:

> > > period_index = pandas.period_range('2012/6/3', periods=10, freq='W-FRI')
> > > <class 'pandas.tseries.period.PeriodIndex'>
> > > freq: W-FRI
> > > [02-Jun-2012/08-Jun-2012, ..., 04-Aug-2012/10-Aug-2012]
> > > length: 10

Although the frequency is "W-FRI", the start dates listed (02-Jun-2012, ..., 04-Aug-2012) are Saturdays.

Converting the frequency of the PeriodIndex to daily using "start", you get Saturdays:

> > > period_index.asfreq(freq='D', how='start')
> > > <class 'pandas.tseries.period.PeriodIndex'>
> > > freq: D
> > > [02-Jun-2012, ..., 04-Aug-2012]
> > > length: 10

And if you convert the PeriodIndex to a DatetimeIndex using to_timestamp(), you get a frequency that is explicitly "W-SAT":

> > > period_index.to_timestamp(freq='D', how='s')
> > > <class 'pandas.tseries.index.DatetimeIndex'>
> > > [2012-06-02 00:00:00, ..., 2012-08-04 00:00:00]
> > > Length: 10, Freq: W-SAT, Timezone: None
