Added conditional for the phonon backend plugin.

If on APPLE, the phonon backend plugin is set to phonon_qt7. If on WIN32, the phonon backend plugin is set to phonon_ds9. I did not add any for generic UNIXes as they could have a whole host of things. A more comprehensive script would actually attempt to detect which phonon plugins were installed. However, this is a simple fix for now that will work for most people.

Modules/FindQt4.cmake

@@ -1059,7 +1059,11 @@ IF (QT_QMAKE_EXECUTABLE AND QTVERSION)
   SET( QT_IMAGEFORMATS_PLUGINS qgif qjpeg qmng qico qsvg qtiff  )
   SET( QT_INPUTMETHODS_PLUGINS qimsw_multi )
   SET( QT_MOUSEDRIVERS_PLUGINS qwstslibmousehandler )
-  SET( QT_PHONON_BACKEND_PLUGINS phonon_qt7 )
+  IF(APPLE)
+    SET( QT_PHONON_BACKEND_PLUGINS phonon_qt7 )
+  ELSEIF(WIN32)
+    SET( QT_PHONON_BACKEND_PLUGINS phonon_ds9 )
+  ENDIF()
   SET( QT_SCRIPT_PLUGINS qtscriptdbus )
   SET( QT_SQLDRIVERS_PLUGINS qsqldb2 qsqlibase qsqlite qsqlite2 qsqlmysql qsqloci qsqlodbc qsqlpsql qsqltds )