Fix interlaced processing

Updating vi2 before creating the TurnsTile instance fixes packed clips,
and using the proper pitch arguments to fillTile fixes planar
processing.
Refine auto tile size calculation

Check that adjusted default tile width and height are multiples of the
minimum size for each axis. Helps with some interlaced tile sizes.
Improve CLUTer code presentation

Function order, variable names, whitespace. Cosmetic.
Update Avisynth header to SEt's 2.5.8 MT version

Also relocate header to new directory, and move include directive to
separate file in preparation for other host support.