HR bugfix - #186649 (Find usages hung on invoking menu)

https://netbeans.org/bugzilla/show_bug.cgi?id=186649

Description: find usages (or any other foreground user activity) is 
blocked by background task. The task is computing of "overridden 
annotation", presumably on java.lang.Object, which is slow. The reason 
why the background task was not canceled is unknown. The problem is 
presumably random and rare. The proposed workaround is to disable 
computation of overridden annotations on j.l.Object. It is currently too 
slow to be useful anyway. The effect should be that the background tasks 
will be fast enough so even in case canceling will not work, the IDE 
will not stop for a long time.

Impact: the IDE appears to be unresponsive to the user. Even if this 
happens rarely, when it happens the IDE is no longer usable.

Risk assessment: the fix should not affect any other class than 
j.l.Object, on which the overridden annotations and go to implementation 
actions will not work.

Reviewed by Tomas Zezula and Peter Pis.

http://hg.netbeans.org/jet-main/rev/e82ee727ac59

Thanks for review,
     Jan