digital: updated qa_mpsk_receiver to have similar tests in test01 and test02.

This is based of and should fix issue #569.
digital: on 32-bit machines when M=4 using single-precision float was causing k=1. Using double-precision calculation here to avoid possible confusion and errors
Merge branch 'maint'
qtgui: explicitly use this pointer in constructing validators. Support for older versions of QT.