Extract a bit of duplicated code in libsvn_ra_serf to a helper function.

* subversion/libsvn_ra_serf/inherited_props.c
  (get_iprops_via_more_requests): Use svn_ra_serf__context_run.

* subversion/libsvn_ra_serf/lock.c
  (run_locks): Use svn_ra_serf__context_run.

* subversion/libsvn_ra_serf/ra_serf.h
  (svn_ra_serf__context_run): New function.

* subversion/libsvn_ra_serf/update.c
  (finish_report): Use svn_ra_serf__context_run.

* subversion/libsvn_ra_serf/util.c
  (svn_ra_serf__context_run): New function, extracted from...
  (svn_ra_serf__context_run_wait): ... this function.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1553932 13f79535-47bb-0310-9956-ffa450edef68