Doesn't handle invalid version numbers

python-debian doesn't handle invalid revision numbers:

Traceback (most recent call last):
  File "./import_package.py", line 364, in <module>
    sys.exit(main(*sys.argv[1:]))
  File "./import_package.py", line 351, in main
    import_package(package, distro, package_url)
  File "./import_package.py", line 327, in import_package
    update_db.import_package(local_dsc_path)
  File "plugins/builddeb/import_dsc.py", line 1707, in import_package
    versions = cl.versions
  File "/srv/package-import.canonical.com/scripts/python-debian/debian_bundle/changelog.py", line 476, in get_versions
    return [block.version for block in self._blocks]
  File "/srv/package-import.canonical.com/scripts/python-debian/debian_bundle/changelog.py", line 143, in _get_version
    return Version(self._raw_version)
  File "/srv/package-import.canonical.com/scripts/python-debian/debian_bundle/changelog.py", line 64, in __init__
    self.full_version = version
  File "/srv/package-import.canonical.com/scripts/python-debian/debian_bundle/changelog.py", line 93, in __setattr__
    raise VersionError(version)
debian_bundle.changelog.VersionError: Could not parse version: 2.0.37+cvs.JCW_PRE2_2037-1

e.g. apache2