Don't show "Running Launch" dialog again after "Checkout Conflicts"

See bug report for how to reproduce.

Bug: 446092
Change-Id: I439bd642341976057305d503a6c769cbb2395f5d
Signed-off-by: Robin Stocker <robin@nibor.org>
Optimize RevUtils.isContainedInAnyRef by not checking older refs

Same optimization as in JGit's RevWalkUtils.findBranchesReachableFrom.
We could also use JGit's method directly, but that does more than what
we need here (it checks all refs).

Change-Id: I80cbd1a732141ac9c3484c14e2b469219f1ddd77
Signed-off-by: Robin Stocker <robin@nibor.org>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>