Python 3 compatibility: Update calls to exec().
Python 3 compatibility:
Update calls to exec().

* subversion/tests/cmdline/svntest/main.py: Update calls to exec().

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