MSVC: Fix debug build
Picomodel: .skin files support

Added support for .skin files (darkplaces-format) to picomodel. Tested
with MD3 and ASE models.
-
Misc_model and shader enhancements patch:

- Using skin, _skin fields to set up a skin number (remaps model surface
textures). Max 256 skins allowed.
- Now using "frame" entity key for framenum. _frame is still supported
and it is an override field (if both "_frame" and "frame" is set,
bloodmap will use "_frame").
- Now there can be up to 9 _foliage.reg files (_foliage, _foliage2,
_foliage_3 ... _foliage9), which are added sequentally.
- ProcessDecorations: fix a crash with empty groups
- misc_model: new "_pushvertexes"/"_pv" field which stands for  "fatboy"
modificator - vertex origins get pushed by their normals. Value can be
both negative and positive.
- misc_model: new "uvautoscale"/"_uvas" field which auto-scales surface
texture coordinates by model scale.  Useful for variable-scale stone
models.
- shaders: added "q3map_colorMod invert", "q3map_alphaMod invert" which
inverts the vertex color data.
Fresh win32/win64 builds