Commits below update xawtv to latest upstream version 3.102

Version in the tree no longer works with current kernel as it doesn't support v4l2. So updated as I needed a quick check if a webcam worked. 

In doing so cleaned up the ebuild and checked use-flags and dependencies, but can't do much testing beyond saying that it works well enough for me. 

Fixes gentoo bug https://bugs.gentoo.org/show_bug.cgi?id=358013