Make XDelta operation simpler, faster and somewhat more effective: * for lookup, use blocks with exactly MATCH_BLOCKSIZE only   (might miss a sub-length match at the end of *both* windows    -> rare and less than 60 bytes worst-case overhead per window) * make blocks hash table support multiple blocks with the same   Adler32 sum but different content (little actual overhead because   the content needs to be compared anyways; very useful for large   values of SVN_DELTA_WINDOW_SIZE)
Make XDelta operation simpler, faster and somewhat more effective:
* for lookup, use blocks with exactly MATCH_BLOCKSIZE only
  (might miss a sub-length match at the end of *both* windows
   -> rare and less than 60 bytes worst-case overhead per window)
* make blocks hash table support multiple blocks with the same
  Adler32 sum but different content (little actual overhead because
  the content needs to be compared anyways; very useful for large
  values of SVN_DELTA_WINDOW_SIZE)

* subversion/libsvn_delta/xdelta.c
  (adler32.len, adler32_in, adler32_out): unused -> remove
  (adler32_replace): adapt doc string
  (init_adler32, init_blocks_table): use fixed block size
  (blocks, add_block, find_block): support multiple entries per adler32 value
  (match_length): fix commentary
  (find_match): use fixed block size; reduce signature
  (compute_delta): use fixed block size only; reduce number of local variables

git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@1054577 13f79535-47bb-0310-9956-ffa450edef68

wbond/subversion,wbond/subversion,YueLinHo/Subversion,YueLinHo/Subversion,wbond/subversion,YueLinHo/Subversion,wbond/subversion,YueLinHo/Subversion,YueLinHo/Subversion,wbond/subversion,YueLinHo/Subversion,YueLinHo/Subversion,wbond/subversion,YueLinHo/Subversion,wbond/subversion