ipc.c: Fix bug where we don't return the correct error code when client

ipc.c: Fix bug where we don't return the correct error code when client
       gives a too-small buffer for share info. Fix from Gil Kloepfer <gil@arlut.utexas.edu>
smb.h:
server.c: Fix for a nastly little security problem with multi-user Windows NT
          servers and Samba where the contents of the open-file cache can end
          up being served out to users who shouldn't have access. This is some
          *seriously* ugly code.
Jeremy.