Added back groupname map stuff removed by Andrew's "slash 'n' burn"

Added back groupname map stuff removed by Andrew's "slash 'n' burn"
tactics :-). Protected by #ifdef until used.

Fixed bug in fd_attempt_close() where a pointer to potentially
free'd memory was returned. I hate that.

Added "blocking locks" as a per-share option for performance testing.

Changed is_mangled() so it will return true if called with a pathname
and any component of the pathname was mangled (it was already attempting
to do this, but not checking for a '/' as end-of-mangle).

This should be a better fix for the wierd stat cache bug Andrew identified.

Jeremy.
(This used to be commit 0de01f45980c7bc261248a9cead972a8d8cbd594)