PMX importer: Sphere map support and fixes for material setup.

I added sphere map support to the PMX/PMD importer.  Also, I noticed there are several issues in the importer so fixed them.

Fix 1 (722b98e): Don't set alpha=0.0, and use blend type "Multiply".  I experienced the problem when importing the Tohoku-Zunko model created by emer (aka gency).  Her hair should be green, but it actually became white.

Fix 2 (dd2df08): Use texture coordinates "NORMAL" for sphere maps.  Sphere maps were not setup correctly.  You can confirm the problem happens to many MMD models such as mamama's GUMI V3 by and kio-miku.

Fix 3 (b813dec): More fixes for previous commit.  I forgot to add support for .spa file, and .sph was supported only for .pmd file, not for pmx file.

Fixes 4-6 (057b7da, 70ef74a, 90cc1c9): Fixes and cleanup for own previous commits.

Fix 7 (6f06e7a): Add options to specify influences of sphere maps.

Fix 8 (55c5da8): The similar fixes for color/alpha settings in Cycles converter.

Fix 9 (859dbbd): Enable "Receive Transparent" for all materials.  Blender does further calculations when enabling "Receive Transparent", but some MMD models need this for rendering shadows accurately.

Fix 10 (77d8bb4): Forgot to add debug prints for sphere textures to pmx loader.

Fixes 11-12 (076928f, 9198f83): Set some more material parameters related to shadows, according to flags in pmx materials.  These changes make the rendering more accurate and slightly reduce the calculations.  Note that "Cast Buffer Shadows" doesn't affect ray tracing, so we still have to disable "Traceable" manually to disable the ray shadows.

Fix 13 (bfed92e): Add option to specify if textures use MIP maps.  Please render ゆきはね13式ミク with this option ON/OFF and compare her eyes between the two renders.  You should understand why this option is needed.


I made the changes for the master branch, but maybe they can be applied also to the 0.5.0-dev branch.


emer's Tohoku Zunko model: http://blender.rgr.jp/
mamama's GUMI V3 model: http://3xma.blog49.fc2.com/blog-entry-16.html
kio-miku model: http://kiomodel3.sblo.jp/article/29725784.html
yukihane13 Miku: http://www.nicovideo.jp/watch/sm21886582