* apt-pkg/deb/debversion.cc:

* apt-pkg/deb/debversion.cc:
  - consider absent of debian revision equivalent to 0 (Closes: #573592)

This moves the existing testcase for version comparison to "my" directory,
adds a few more tests (e.g. the tests used in cupt) and rewrites the
testcases runner: The runner does now call dpkg --compare-versions
to check what dpkg thinks about the comparison - all done in less code ;)