Move PORTREVISION from multimedia/avidemux/Makefile.common into the
three slave ports multimedia/avidemux-cli, multimedia/avidemux-plugins,
and multimedia/avidemux-qt4. Ensure they are properly set there
after revision 464084.

That way any sweeping changes (using Tools/scripts/bump-revision.sh
or similar in particular) have a chance of working or at least flagging
a potential issue.

PR: 226533