Make FSFS code write deltified representations.  This is in large parts copied from make-revs.c in r9474.
Make FSFS code write deltified representations.  This is in large
parts copied from make-revs.c in r9474.

   * subversion/libsvn_fs_fs/fs_fs.c
     (struct rep_write_baton): Added new fields to support writing of
       deltas.
     (rep_write_contents): Write to the delta stream if it is
       available.
     (choose_delta_base): New, selects a representation to base the
       delta off of, copied from make-revs.c.
     (rep_write_get_baton): If this is a delta instead of plaintext,
       set up the appropriate delta writer interface.
     (rep_write_contents_close): Find the size of the svndiff binary
       data, and always write a cosmetic "ENDREP".

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