Remove unused string.
Avoid using hardcoded URL for the website.
Graph builder: Weaken the filter duplication check introduced in 2ccec30a86a326a86af9649ba5b0695c17f90cc8.

Only check for duplication if we already have the same filter with a DO_NOT_USE merit. In other cases, the merit based ranking tells us which filter should be chosen.

This commit fixes the case where external filters were not used although their internal counterparts were disabled.
remove custom code
update CFLAGS and ffmpeg/config.asm and ffmpeg/config.h
update ffmpeg (n0.8-19580-g28adecf)

Notes: broken atm because our custom files need to be updated too

* libavcodec/h264_dxva.c
* libavcodec/h264_recov.c
* libavcodec/vc1_dxva.c