Minor xdelta optimization: find short matches at both end of the delta window.
Minor xdelta optimization: find short matches at both end of the delta window.

* subversion/libsvn_delta/xdelta.c
  (reverse_match_length): new symmetric counterpart to match_length
  (store_delta_trailer): new utility to find matching ranges at the end of a buffer
  (compute_delta): prefix and postfix optimization

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion