Work around problem where 'del os.environ["FOO"]' doesn't update environment.
test-hook failed since changeset 949516072388 because of this on Solaris 8.
abort: repository a not found!
255
abort: error: Connection refused
255
abort: repository a not found!
255
abort: destination '../a' already exists
255
abort: repository a not found!
255
destination directory: q
abort: destination 'q' already exists