Right now, bdist_msi can run out of memory when used for larger
packages. (I found this problem working with NLTK.) The solution is
really simple - just add a db.Commit() so that stuff gets flushed to
disk more often. The attached patch does just that.

I set this as a release blocker because I think shipping Python 3.1 with
a bdist_msi in that doesn't work for large packages is probably a
mistake, and the patch to fix it is small and non-invasive.