Update busyChanged docs
Update busyChanged docs

The signal is poorly named. It's not a NOTIFY signal. Rather, it means
a previously-busy sensor is now free. Only useful if the system has
exclusive access sensors.

None of the current backends support exclusive access.

Fixes: Maemo Bug 236535

qtproject/qt-mobility,qtproject/qt-mobility,KDE/android-qt-mobility,enthought/qt-mobility,enthought/qt-mobility,qtproject/qt-mobility,kaltsi/qt-mobility,kaltsi/qt-mobility,enthought/qt-mobility,tmcguire/qt-mobility,KDE/android-qt-mobility,enthought/qt-mobility,kaltsi/qt-mobility,tmcguire/qt-mobility,tmcguire/qt-mobility,KDE/android-qt-mobility,qtproject/qt-mobility,kaltsi/qt-mobility,tmcguire/qt-mobility,qtproject/qt-mobility,tmcguire/qt-mobility,enthought/qt-mobility,kaltsi/qt-mobility,qtproject/qt-mobility,KDE/android-qt-mobility,kaltsi/qt-mobility,enthought/qt-mobility