Partly implements issue #3372: When building the rep state read sequence along the skip-delta chain, re-use file instances that pertain to the same pack file.
Partly implements issue #3372: When building the rep state read
sequence along the skip-delta chain, re-use file instances that
pertain to the same pack file.

* subversion/libsvn_fs_fs/fs_fs.c
  (create_rep_state_body): re-use the last file instance, if possible
  (create_rep_state): extended docstring to cover new parameters
  (build_rep_list): provide hints
  (read_window): seek before read as the file object may be shared
  (svn_fs_fs__get_file_delta_stream, 
   verify_walker): adapt callers not using hints


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@1381938 13f79535-47bb-0310-9956-ffa450edef68

YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion