Eliminate some small-read and small-write performance issues in FSFS.
Eliminate some small-read and small-write performance issues in FSFS.

* subversion/libsvn_fs/fs_fs.c
  (svn_fs_fs__put_node_revision, svn_fs_fs__create_txn,
  get_txn_proplist, svn_sf_fs__change_txn_prop, write_next_ids,
  svn_fs_fs__set_entry, svn_fs_fs__add_change, rep_write_get_baton,
  svn_fs_fs__commit, svn_fs_fs__set_uuid): Open files in buffered
  mode.
  (write_next_ids): Close the file when we are done.


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@852970 13f79535-47bb-0310-9956-ffa450edef68

YueLinHo/Subversion,wbond/subversion,wbond/subversion,wbond/subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,wbond/subversion,wbond/subversion,wbond/subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,wbond/subversion