(vc-name): Moved from vc.el; vc-rcs-status now uses it.

(vc-name): Moved from vc.el; vc-rcs-status now uses it.
(vc-name, vc-backend-deduce): Set both vc-name and vc-backend
properties, to avoid calling vc-registered unnecessarily when
the other property is needed.
(vc-rcs-status): Yield only status of locks; do not try to yield " REV"
if there are no locks, since this cannot be done easily if there are
branches.  Use vc-name instead of duplicating its function incorrectly.
Fix off-by-one bug when inserting master header pieces.  Read headers
8192 bytes at a time instead of 100.  Don't bother to expand-file-name.
(vc-rcs-glean-field): Removed.