Fix a few things in ExclusiveGroup documentation.

Change-Id: I4feda741c7052e06f066c2ea69ba242a11b62b04
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@digia.com>
Merge remote-tracking branch 'origin/release' into stable

Change-Id: I32b905b74cf7f7c5dc9b9d93900950d0f742ce70