Followup to r1333602: don't keep installing handlers. One is more than enough! (symptom: massive repeat of output)
Followup to r1333602: don't keep installing handlers. One is more than
enough! (symptom: massive repeat of output)

* subversion/tests/cmdline/svntest/main.py:
  (execute_tests): only add a handler if the current set is empty

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