NB 7.2 HR integration review request: 212953

Description:
http://netbeans.org/bugzilla/show_bug.cgi?id=212953

A memory leak fix caused that classloader used for loading custom user 
components in GUI builder sometimes expired too soon and the new instance 
caused mismatch in the complicated UI defaults swapping machinery. This made 
the use of SwingX components often fail to instantiate and so difficult to use 
in the GUI Builder.

The fix is easy: making sure the classloader instance remain the same while 
the form is opened, as it used to be in previous releases.

Fix verified by the reporter, changeset reviewed by Jan Stola.

Risk assessment: low risk

Changeset: http://hg.netbeans.org/main-golden/rev/a2f8994a7d18

Thanks for the review,
Tomas