[mythtv] Updates to mythtv/external and required system libraries

[Gary Buhrmaster]

On Mon, Aug 6, 2018 at 2:57 AM Gary Buhrmaster
<gary.buhrmaster at gmail.com> wrote:
> ... and is why I (knowingly)
> explicitly decided to update the mythtv external library rather
> than even considering using a system library which could at
> some point be the wrong version.

btw, looking back at that trac ticket, I think I actually sent
in some wrong patches, but the goal was correct
(don't depend on the system libraries).