Revision 1683378

Prevent a possible FSFS repository corruption with power or network disk
failures during 'svnadmin pack'.

* subversion/libsvn_fs_fs/pack.c
  (close_pack_context): Call svn_io_file_flush_to_disk() for pack file.
  (pack_phys_addressed): Use svn_io_file_open() to open pack and manifest 
   file and call svn_io_file_flush_to_disk() before closing them.

* subversion/libsvn_fs_fs/revprops.c
  (svn_fs_fs__copy_revprops): Use apr_file_t to write pack file and flush
   changes to disk before close.
  (svn_fs_fs__pack_revprops_shard): Use svn_io_file_open() to packed revision
   properties manifest file and call svn_io_file_flush_to_disk()
   before closing it.