(PUP-2562) Remove uses of unsupported range syntax in PMT.

Prior to this commit, if any module contained a dependency statement
without a version requirement, it was erroneously treated as if no
version would satisfy (rather than allowing any version to satisfy).
This was a regression, and this change abstracts the places where we
made those checks, and corrects the error. In addition, there is new
debugging output that will help identify similar cases in the future.