CHG: only double framerate if material is interlaced

[koying]

@davilla You opinion on this?
The idea is:

1. try harder to find out interlaced
2. if interlaced, double the fps
3. if not, adjust refresh rate to closest, not doubled

If think those "motion smoother" TV algorithms get confused with, eg 25 fps on 50Hz, so induce hiccups

[davilla]

Sure, defaulting to a double value was originally to keep gui updates smooth.
The only real issue with interlace detection are those odd h264's that 'might' be interlaced and you can only tell when actually decoding.