2552 smbfs: add support for NFS-like remove
This is (mostly) work from Jilin Xpd jilinxpd@gmail.com

done during the 2012 Google Summer of Code program.

I finished it up, did some debug and testing etc.
Note that there remain several XXX marks and such in the code after this change.

I've postponed cleanup of those until after the mmap work to avoid making it

harder to merge that (much larger) work.

There are some STC-derived tests for this (to be integrated separately).