Simplify the mutexpool used in QObject.

Simplify the mutexpool used in QObject.

Since we now have QBasicMutex as a POD, we can simplify the mutexpool.
This remove the call the the Q_GLOBAL_STATIC and some others tests that
are taking CPU cycles when activating a signal.

The QMutexPool class itself can't be simplified because its mutex are
recursive mutexes, and the size is dynamic. also it is harder to get all
the mutexes initialized to 0.

Change-Id: Ie781655635907d2ad620eb189099cba14638414f
Reviewed-by: Bradley T. Hughes <bradley.hughes@nokia.com>
Reviewed-on: http://codereview.qt.nokia.com/2171
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Olivier Goffart <olivier.goffart@nokia.com>