Allow a little leeway before rejecting double rate deinterlacers (bob/greedyh/yadif)

[mark.kendall@…]

In summary, the nvidia drivers increase the htotal of the accepted modeline to ensure it is divisible by 8. This changes the calculated refresh rate and can lower it below the 2* framerate threshold needed for bob etc.

The attached patch adds a little tolerance to the accept/reject decision to ensure the best deinterlacing options can still be used.

I'm seeing this on several frontends where the EDID reported timings for 50Hz modelines give a refresh rate of 50Hz exactly, but by the time the drivers have adjusted the modeline the refresh rate drops to circa 49.9Hz.

[markk]

(In [19287]) Allow a small amount of tolerance before rejecting double rate deinterlacers due to low refresh rates. This ensures bobdeint etc will still work when the video driver (specifically the nvidia proprietary driver) adjusts the htotal to ensure it is divisble by 8. Closes #4637

[thomas@…]

I applied [19287] to 0.21 fixes and it works there, too. Please backport.