Followup to r36483: fix a reference to a global variable (sigh)
Followup to r36483: fix a reference to a global variable (sigh)

* subversion/tests/cmdline/svntest/sandbox.py:
  (Sandbox.cleanup_test_paths): prefix old global with svntest.main

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