new improved omnitest in customtest.R. this overrides cran version so it...

...'ll work with more complicated function calls. wil and i noticed that we (and  probably sean) had tested this with a developer's version of swirl which has the improved omnitest (with recursive match calls). we incorporated the source code of this improved omnitest in customtest.r for all the lessons (except the introduction) so that there shouldn't be any false negatives (LOL) when testing.