* subversion/libsvn_client/ra.c (callback_baton_t): Add 'wcroot_abspath' member. (get_wc_contents): New function. (svn_client__open_ra_session_internal): Initialize new 'get_wc_contents' baton member.
* subversion/libsvn_ra_serf/update.c (report_ctx_t): Add 'cached_contents' member. (local_fetch, handle_local_fetch): New functions. (fetch_file): Use the 'get_wc_contents' RA callback to check for a local copy of the file contents whose SHA1 checksum we are about to fetch from the server. If we've got those contents already, read them (via the callback-returned stream) instead of from the network.