QMutex is now just a pointer

QMutex is now just a pointer

And added a POD QBasicMutex. (QBasicMutex* can safely be
static_cast'ed to QMutex*)

The d pointer is not anymore always a QMutexPrivate.

If d == 0x0: the mutex is unlocked
If d == 0x1: the mutex is locked, uncontended

On linux:
if d == 0x3: the mutex is locked contended, waiting on a futex
If d is a pointer, it is a recursive mutex.

On non-linux platforms:
When a thread tries to lock a mutex for which d == 0x1, it will try to
assing it a QMutexPrivated (allocated from a freelist) in order to wait
for it.

Change-Id: Ie1431cd9402a576fdd9a693cfd747166eebf5622
Reviewed-by: Bradley T. Hughes <bradley.hughes@nokia.com>
Reviewed-on: http://codereview.qt.nokia.com/2116
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Olivier Goffart <olivier.goffart@nokia.com>