I wrote a test for FileContentsBrowser>>changeMessageCategories: but to 
my surprise I get a DNU: FileContentsBrowser doesn't understand #unlock.

I have three implementors of #unlock in my (trunk) image, namely,
* Morph>>unlock
* SystemWindowButton>>unlock
* View>>unlock

Of course, a FileContentsBrowser is a Browser is a CodeHolder is a... 
none of these.

I've recorded the problem on Mantis 
(http://bugs.squeak.org/view.php?id=7615). I guess no-one used a 
FileContentsBrowser like this before? My image has no history for this 
method.

frank