review for 196940

Hi all,
i'm asking for review of a fix for 
http://netbeans.org/bugzilla/show_bug.cgi?id=196940 ~ 
http://hg.netbeans.org/main/rev/65b15c2782c0 so i can integrate into 70.

Issue description:
When using tab completion in the File Name field in the Directory 
Chooser (File -> Open Project...), the dir chooser did some IO 
operations (namely java.io.File.listFiles) in AWT. This caused IDE hang 
(in some cases even the whole gnome session) when a symbolic link to a 
NFS drive on currently inaccessible server was touched by 
java.io.File.listFiles.

Impact assessment:
IDE is frozen for a significant amount of time (may be a several minutes 
depending on the value of timeout when an OS FS gives up) and has to be 
usually forcefully killed. According to one of user reports sometimes is 
hung also the whole X windows system and the IDE has to be killed from 
another session.

Risk assessment:
No risk i can think of. The slow piece of code is just moved to a 
background thread (that had already been there anyway).

Fix:
java.io.File.listFiles and the code filtering it's result was moved from 
the EDT to an already present background thread.