Eliminate most of the overhead introduced by batch fsync'ing in FSX when we actually only fsync a single file. 
Eliminate most of the overhead introduced by batch fsync'ing in FSX when
we actually only fsync a single file. 

* subversion/libsvn_fs_x/batch_fsync.c
  (svn_fs_x__batch_fsync_run): Fall back to ordinary foreground processing
                               when there is nothing to parallelize.

git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@1711374 13f79535-47bb-0310-9956-ffa450edef68

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