Revision 1680819

Prevent a possible FSFS repository corruption with power or network disk
failures when changing revision properties. Perform a hardware flush
after we finished writing to a temporary revprop file and before moving
it into place. The change doesn't affect commit operation behavior.

The corruption can be easily reproduced by triggering a power loss while
performing svnsync.

This change is somewhat similar to what we did in r1483781, but covers how
we write revision property files. See related discussion in dev@s.a.o
(Subject: "FSFS Repository corruption on high load on Windows [...] ") [1].

Patch by: me
          kotkov

[1] http://svn.haxx.se/dev/archive-2013-05/0245.shtml

* subversion/libsvn_fs_fs/revprops.c
  (repack_stream_open): Rename the function ...
  (repack_file_open): ...to this. Rework it to return files (apr_file_t)
   instead of streams.
  (repack_revprops): Work with a file instead of a stream. Flush any
   unwritten data to disk before returning.
  (write_non_packed_revprop): Flush any unwritten data to disk after
   serializing the revision property list.
  (write_packed_revprop): Cope with the changes in repack_file_open() and
   repack_revprops() that now work with files. Flush the data to disk when
   done writing to a temporary manifest file.