This renames vo_gl3 to vo_opengl, and makes it the default. The old
vo_gl is still available under "opengl-old".
We keep "gl3" as alias to "opengl" for short-term compatibility.
For OSX/Cocoa, the autoprobe order changes (prefer the "opengl" over
"opengl-old").
Remove "gl_nosw". This was a compatibility alias for "opengl-old", and
there's no point in keeping it.
af_format.h declares some symbols which are defined in format.c. The
fact that af_format.c is a completely unrelated file is rather
confusing. Having the header and implementation file use the same base
name is more uniform. (af_format.c is the audio conversion filter, while
af_format.h and format.c are about audio formats and their properties.)
Also fix all source files which include this file.
