qtgui: enables use of QWT 6.1.
filter: fixed issue with resampler using buffer size information (always a mistake).

The intent was to ask the scheduler for the maximum amount of data. Now, it plays it safe by asking for just enough the next time. Performance tests show it works well.
qtgui: enables use of QWT 6.1.
Merge branch 'master' of git.gnuradio.org:gnuradio
Merge branch 'maint'
Merge branch 'master' into next