Fix for #184430 - "Check for External Changes" progress shall not hide other (more important) progresses

#184430:  "Check for External Changes" progress shall not hide other 
(more important) progresses

Self explaining, "Check for External Changes" is displayed too 
aggressively and hides more important tasks. Fix is not trivial, but 
straightforward, functionality verified and risks minimal. Fix improves 
selection policy of progress UI - now tasks which are not "suspended" 
have bigger display priority, so that "suspended' task could never hide 
regular one.

http://hg.netbeans.org/core-main/rev/31e1f5bb3cc1

Thanks,

Dafe//