pahole: hole removals

reuse padding for good. No speed changes expected.
pahole: remove the flat shading field

why do not reuse one of the vertex lightining field?
pahole: remove the Environment mapping support

unused, probably not yet needed. Allow to do further optimization
which are the real driver behind this patch.
pahole: reorganize Face to fit in just 2 cacheline

dropping the Environment Mapping support code, although
not yet needed, was a necessary evil.
Measurable speedup achieved.
pahole: reindent
pahole: reorganize the cacheline usage

move the huge children array to the bottom so we can
access all the other fields with more ease.
pahole: reuse the padding space for good.
pahole: TEXENV enum is no longer needed

Even before to drop the Environment Mapping support.
move the spline code into the extension library
Merge branch 'pahole'