more corrections

* Initial release (Closes: #730568)
* debian/control: Changed chort description of each package to be unique
* debian/patches: Fix patches to apply cleanly
* debian/copyright: Clarify license for most files as GPL-3+, drop text
* debian/copyright: Clairfy signal.py license as GPL-3 (only)
* debian/copyright: Add funcsigs license
* debian/copyright: Add mock license
* debian/copyright: Add extcmd license
* debian/python3-plainbox.lintian-overrides: Remove override for licenses
  removed by the 03-unvendorize patch.