Simplify file contents comparisons.
Simplify file contents comparisons.

* subversion/tests/cmdline/externals_tests.py:
  (checkout_with_externals, update_receive_change_under_external,
      export_with_externals, external_with_peg_and_op_revision,
      new_style_externals, can_place_file_external_info_dir_external):
    simplify/revamp the file contents reading and comparison.


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@931780 13f79535-47bb-0310-9956-ffa450edef68

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