Have distclean target keep up with build improvements

If you run `cmake --build . -- distclean` all generated files will
now be gone! This adds the files that have been introduced in later
improvements to the build system.
Merge pull request #309 from rolk/309_clean

Have distclean target keep up with build improvements
Merge remote-tracking branch 'upstream/master'
Merge branch 'master' into devel