a major share modes reorganisation.

a major share modes reorganisation.

The shares modes code is now split into separate files. The shared
memory implementation is in locking_shm.c. The slow implementation is
in locking_slow.c

It is all controlled by a struct share_ops structure that has function
pointers to the implementation of all the functions needed by a share
modes implementation. An initialisation function sets up this
structure. This will make adding new implementations easy and clean.

This also allowed me to get rid of the ugly code in smbstatus. Now
status.c links to the locking code and calls methods in share_ops.

I also renamed some things and generally organised things in a much
cleaner fashion. Defines and structures specific to each
implementation have been moved to the appropriate file and out of
smb.h.