Don't count unscaled frequently changing texels.

May cause more things to be scaled per frame (especially if first textures
on a frame are frequently changing.)
Forgive freq. changed tex if they mend their ways.
Reduce change frequency limit for texscaling.

Since we have the texels limit now, this should allow more textures to be
scaled safely.  Also, it may detect alpha optimizations in more textures,
since we currently skip them for frequently changed textures.
Merge pull request #6321 from unknownbrackets/texscaling

Reduce some texture scaling limits to rely on texels instead