Check the python extension in travis

Under the travis environment, the python FF extension is for some reason
installed to /usr/local/lib/python3/dist-packages instead of say
/usr/local/lib/python3.2/dist-packages. The former is not in the default python
site-packages path, so it must be manually added.

testing

more test

Fix typo; expedite python3 path checking

Cleanup the script [ci-skip]
Merge pull request #1498 from jtanx/pyext-travis

Check the python extension in Travis.