Add diagonal combing detection

[dimag0g]

This PR modifies the combing detection algorithm metric=1 to better detect combing along diagonal lines. Since the algorithm detects extra pixels as combed (in addition to those detected by the base algorithm), the MI value must be increased to compensate.

Currently there's only the C implementation. If the changes are deemed worthy, we can discuss the SSE2 implementation.

Here are some screenshots for comparison, produced by:

left=FFVideoSource(FileName).TFM(pp=1, metric=1, opt=0, MI=85, display=true).TDecimate()
right=FFVideoSource(FileName).TFM(pp=7, metric=1, opt=0, MI=85).TDecimate()
StackHorizontal(left, right)

This PR, clean frame correctly detected

This PR, combed frame correctly detected

This PR, combed frame correctly detected

Base algorithm, clean frame detected as combed

Base algorithm, combed frame not detected

Base algorithm, combed frame not detected