svntest: When runing 'svn merge -rREV1:REV2 URL DIR', allow the '-r' parameter to be optional.
svntest: When runing 'svn merge -rREV1:REV2 URL DIR', allow the '-r'
parameter to be optional.

* subversion/tests/cmdline/svntest/actions.py
  (run_and_verify_merge): Update doc string.
  (run_and_verify_merge2): Update doc string, and adjust
   implementation to handle the the optional REV1/REV2 parameters.

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion