missed a few checks for spotless before calling trigpoly
resolves #286 on build servers by not recreating the file if it already exists in the tmp directory.  note that it could still fail on the very first parallel tests of a build server, but this will be good enough.  it's a pain to do better, since stl2vrml takes an output directory, not a filename.  (certainly not very difficult to do better, but this feels like a reasonable compromise)
fix win32 mexw32 output directories
adds unit test that would have caught the missing checkDependency
Merge pull request #425 from RussTedrake/lecture

minor fixes