Add additional CMake check for PulseAudio support.
Add additional CMake check for PulseAudio support.

Problem was that our code needs the method enable() in Phonon's
pulsesupport.h. Now we check for the presence of this method before
enabling PulseAudio support.

BinChengfei/phonon-vlc,panzi/phonon-vlc,BinChengfei/phonon-vlc,panzi/phonon-vlc,KDE/phonon-vlc,KDE/phonon-vlc,BinChengfei/phonon-vlc,KDE/phonon-vlc