"master" file system and refreshing

I found another annoyance with the master file system in the projects
dev builds.  It seems that the file system memorizes contents of a
directory.  I have a directory with contents:
  ~/project/lib
     mylib.jar 
     myxmltranslator.jar
and I add these to the project via the add resources wizard.  Now, I
find that I need to add another jar file (foo.jar) to this directory. 
When I go though the add resources wizard, I don't see foo.jar.  I also
don't see any way to refresh the file system.  If I restart, I do see
foo.jar in the wizard.

Is there some way to refresh the master file system?