Follow-up to r29231, making sure that every svn_ra_neon__request_t is

Follow-up to r29231, making sure that every svn_ra_neon__request_t is
explicitly destroyed even when errors are thrown.  In two cases, this
means adding blatantly missing svn_ra_neon__request_destroy calls; in
the rest it just means changing SVN_ERR calls to "if (err) goto
cleanup" and the like.

(Full disclosure: I'm not going to be at the machine where I have
davautocheck working until Monday, so this hasn't actually been fully
tested yet.)

* subversion/libsvn_ra_neon/commit.c
  (do_checkout, commit_delete_entry, commit_close_file): Always
   destroy the request.

* subversion/libsvn_ra_neon/lock.c
  (do_lock, svn_ra_neon__get_lock): Always destroy the request.

* subversion/libsvn_ra_neon/session.c
  (exchange_capabilities): Always destroy the request.

git-svn-id: http://svn.collab.net/repos/svn/trunk@29233 612f8ebc-c883-4be0-9ee0-a4e9ef946e3a