CLI: Avoid redundant 16-bit upconversions in piped raw input

It's not possible to seek in pipes, so if we want to skip frames we have to read and
discard unused ones. It's pointless to do bit-depth upconversions in those frames.
Fix input support from named pipes in Windows
Merge branch 'plain' into 7mod

Conflicts:
	input/raw.c
	input/y4m.c