Finish issue #4179 by eliminating no-op HEAD requests from ra_serf's checkout/update logic.
Finish issue #4179 by eliminating no-op HEAD requests from ra_serf's
checkout/update logic.

* subversion/libsvn_ra_serf/update.c
  (handle_local_contents): Was local_fetch().  Callers updated.  Also,
    decrement the directory reference count.
  (handle_local_fetch): Remove as unused.
  (fetch_file): Avoid HEAD requests where locally cached file contents
    are available.  Instead, either immediately handle the contents,
    or squirrel away some state so we remember to do so...
  (finish_report): ...here.

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion