Rename flac demux plugin to flacsys

Fix typo of [17361]

Closes #758

- Fix file descriptor leak when opening an empty file
- Don't close STDIN.

(of course, it was obvious reverting the earlier fix would break it,
 but some people don't seem to care about the build system as long as
 "their" feature works).
Oh, and don't let version.c twice in CLEANFILES.

* modules/codec/x264.c: Fix range enforcement and string selection (deprecated was in the way). Use actual default values for options direct, me and deblock filter params (mainly for the gui).