Serf now uses one big update request for legacy servers, so the local fetch via
sha1 is only used for new servers. So now is the time to disable the MD5
fallback to avoid possible MD5 collisions.

* subversion/libsvn_wc/wc_db_pristine.c
  (svn_wc__db_pristine_check): Report non-sha1 checksum as missing. Use a
    filestat to avoid an unneeded db transaction for every file on a checkout,
    when using serf with separate requests.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1449564 13f79535-47bb-0310-9956-ffa450edef68