Bump MODULE_VERSION to 5.2.1

Change-Id: Ic460fc350c446a91ef105b7fe92cda937f0ef914
Reviewed-by: Matti Paaso <matti.paaso@digia.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Reviewed-by: Simo Fält <simo.falt@digia.com>
Merge remote-tracking branch 'origin/stable' into dev

Conflicts:
	.qmake.conf

Change-Id: Ib1ccb9d61eee5fc4d007eb19298d4a95ee821b51