Import avidemux build fixes from head.

MFH: r464215 r465620

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

Un-break avidemux and plugins (import C++11 fixes from upstream)

PR: 224384
Submitted by: rkoberman@gmail.com

Approved by: ports-secteam (riggs)