Network filesystem topics

That sounds like a good idea, but in fact just about all of the clients already do case-preserving correctly, so when we get a miss it's *extremely* likely that the file doesn't exist (and the client is just making sure that's so).

These code paths are already some of the most complex in Samba (getting the *absolutely* correct error message returns here is *essential* to make real applications work here) so I'm loathe to add any more complexity here.