This is a fix for the SAR package, whose method 
PositionableStream>>fileInFor:announcing: still used an old 
SystemDictionary method instead of the new SystemNavigation methods.  
This prevented the SUnit package from being installed into a current 
3.6alpha-5240 image, for example.

Hmm, I guess if this change is made to SAR, then it won't work with 
Squeak 3.4, which will prevent people from installing the SqueakMap 
bootstrap for 3.4.  Perhaps a more defensive test needs to be put in 
for the time being... maybe test if the SystemNavigation class is 
present and use that if it is, otherwise use the Smalltalk global 
variable.  Argh.

So, this isn't quite a complete fix.  Goran, we need SM 1.1 pretty soon 
so that we can have different versions of these things... :-)

- Doug Way