reader spiff: fix skip dir marker with invalid len

GPUJPEG v0.27.8

cleanup

Moved the preprocessor common structs to gpujpeg_preprocessor.h and keep
in gpujpeg_preprocessor_common.cuh only utils.

The naming may not be ideal but this is to avoid including the .cuh file
with gpujpeg_common_internal.h for struct gpujpeg_postprocess definition
since gpujpeg_preprocessor_common.cuh file includes gpujpeg_common_internal.h
in turn (for subsampling utility fns).

+ small improvements if recent code (eg. indent)

PAM/Y4M: support for UTF-8 file names

GPUJPEG 0.27.5

refers to GH-93

GPUJPEG 0.27.1

GPUJPEG 0.26.0