On the fsfs-format7 branch:  Add a new file API function that will allow
you to align your file read access properly to the given block sizes.
That's relevant whenever the OS needs to actually ready data from the
drive instead of simply fetching it from its internal cache.

* subversion/include/svn_io.h
  (svn_io_file_aligned_seek): declare new public API function

* subversion/libsvn_subr/io.c
  (svn_io_file_aligned_seek): implement it

* subversion/libsvn_fs_fs/cached_data.c
  (aligned_seek): new local wrapper function
  (open_and_seek_revision,
   open_and_seek_transaction,
   get_fs_id_at_offset,
   create_rep_state_body,
   read_delta_window,
   read_plain_window,
   get_contents): use the new seek function when accessing rev / pack files

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/fsfs-format7@1442910 13f79535-47bb-0310-9956-ffa450edef68