doc/filters: add geq gradient examples

Radial gradient by Víctor Paesa. Linear gradient by Paul Gentemann.

Also-by: Víctor Paesa <victorpaesa@googlemail.com>
Also-by: Paul Gentemann <beriukay@gmail.com>
Signed-off-by: Lou Logan <lou@lrcd.com>
avformat/avienc: Dont search for startcodes in inserted empty avi frames

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>