With n conflicting rules. "conflicting.contains(possible)" has been
observed as severe hotspot in a workspace with n= ~1000 projects,
especially because all n Jobs did the same.

Also avoid second pass if nothing changed.

Functionality is tested with
IJobManagerTest.testTransferToJobWaitingOnChildRule()
OrderedLockTest.testComplex()
DeadlockDetectionTest.testImplicitRules()