QMdiArea: Ignore events of other instances in the event filter.

This caused for example the variable QMdiAreaPrivate::isSubWindowsTiled
being cleared from another instance, which resulted in odd
resizing behavior.

Task-number: QTBUG-31448
Change-Id: I880f7e415d6654e52499df1bfaf99f2c55d86320
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>
Reviewed-by: Andy Shaw <andy.shaw@digia.com>
Avoid showing warnings from drawPixmap when using a QGLWidget

QGLWidget has a paint device type of Widget, yet drawing on it
from outside the gui thread is fine as long as ThreadedOpenGL is
supported. It has probably been overlooked that the device type
OpenGL applies to QGLFramebufferObject and such but not QGLWidget.

This will fix the problem of flooding the output with warnings in
the tst_qglthreads autotest and potentially elsewhere too.

Task-number: QTBUG-38771
Change-Id: Ie014a2610a0db41b31c30c404e286d4997aecdc3
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
Reviewed-by: Gunnar Sletta <gunnar.sletta@jollamobile.com>
Use sched_yield instead of pthread_yield

sched_yield is standardized and on linux pthread_yield is implemented as sched_yield.
Building Qt for Android on OS X doesn't compile with the pthread version.

Change-Id: I1913afa83769805291e987f55b8f452299a43dce
Reviewed-by: Mark Brand <mabrand@mabrand.nl>