On the fsfs-improvements branch:  Align rev / pack file read access to 4k offset boundaries (APR file buffer size default).  This will speed up the common scenario where we navigate "backwards" through a rev file.
On the fsfs-improvements branch:  Align rev / pack file read access to
4k offset boundaries (APR file buffer size default).  This will speed
up the common scenario where we navigate "backwards" through a rev file.

* subversion/libsvn_fs_fs/cached_data.c
  (aligned_seek): new utility function
  (open_and_seek_revision,
   open_and_seek_transaction,
   get_fs_id_at_offset,
   get_root_changes_offset,
   create_rep_state_body,
   auto_read_diff_version,
   read_delta_window,
   read_plain_window,
   get_contents,
   svn_fs_fs__get_changes): use aligned seek when accessing rev files

git-svn-id: 2c7ed5bc06a69ba39b874304b5a8005b1c01e2e4@1504849 13f79535-47bb-0310-9956-ffa450edef68

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