Improve pool usage in RA-serf and RA-local by making use of the scratch pool
that is available during the 'switch' operation since r1449413.

The RA-svn implementation currently has no use for a scratch pool in that
context, so there is no change there.

* subversion/include/svn_ra.h
  (svn_ra_do_switch): State what is allocated in the result pool.
  (svn_ra_get_inherited_props): Tweak the log message for consistency.

* subversion/libsvn_ra_local/ra_plugin.c
  (get_username): Clarify pool usage in the doc string, fix typos, and
    rename 'pool' to 'scratch_pool'.
  (make_reporter): Switch to dual pools.
  (svn_ra_local__do_update,
   svn_ra_local__do_status,
   svn_ra_local__do_diff): Track the change to make_reporter().
  (svn_ra_local__do_switch): Pass the scratch pool to make_reporter().

* subversion/libsvn_ra_serf/update.c
  (make_update_reporter): Switch to dual pools.
  (svn_ra_serf__do_update,
   svn_ra_serf__do_diff,
   svn_ra_serf__do_status): Track the change to make_update_reporter().
  (svn_ra_serf__do_switch): Pass the scratch pool to make_update_reporter().


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1465280 13f79535-47bb-0310-9956-ffa450edef68