Bump MODULE_VERSION to 5.2.1

Change-Id: Ieb54e9508f48cc9694bd9a59dc9908cf84a62486
Reviewed-by: Matti Paaso <matti.paaso@digia.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Merge remote-tracking branch 'origin/stable' into dev

Conflicts:
	.qmake.conf

Change-Id: I0b0d5044d34bc915614253e89fb6029d6bfb75f7