Fix for 236554 - Improve exception notification when assertions are disabled

Hi,

please review the fix for bug #236554

Description of the bug (including IZ #):
#236554 - In 7.4 rc2, reporting and notifying about exceptions differs 
to 7.3 because of new notification center - in 7.4 the icon in bottom 
right corner does not varies according to the last notification as it 
did in 7.3 .

Impact assessment i.e. why it is a showstopper?
For many users new way may not be very intuitive. Reporting bugs is 
essential.

Risk assessment i.e. why is it safe?
No complex logic was changes, just few tweeks of UI panel and icons

Confirmation of peer code review andQE verification of fix (QE adds note 
into comment about verification)
Ondrej Vrabec reviewed the changesets and he agrees with it.

Changeset info (for reviewing diffs):
http://hg.netbeans.org/core-main/rev/9151de0a17e5

Thanks,

Honza