load monkeyYaml without assuming it is on path

use imp to import monkeyYaml even if not on path

This fixes a problem with the fallback YAML parser, in the test suite for the Chromium project.

The test262 runner is able to load monkeyYaml because monkeyYaml.py is in the same directory as test262.py, which is in python's load path.

The Chromium python runner does not add the path to parseTestRecord.py to its load path, making `import monkeyYaml` not work.