test_course() doesn't preserve/reset current lesson

[jonmcalder]

After running test_course(), the current lesson will be the last lesson specified in the manifest file, regardless of what the current lesson was before test_course() was called. This is fine for the general use case, but technically is an unexpected and unwanted "side effect".

[seankross]

Absolutely agree this needs to be fixed.

[jonmcalder]

Cool - have actually just pushed a pretty simple fix for this (but let me know if my approach is incorrect). It's now included as part of pull request #34