Update WebGL 1.0 spec to disallow aliasing among active shader attributes.

See issue #713
Merge pull request #744 from zhenyao/aliasing

Update WebGL 1.0 spec to disallow aliasing among active attributes
Fix tex-new-formats to reflect WebGL2 sRGB semantics, which are different from WebGL1 with EXT_sRGB
Merge pull request #745 from bjacob/fix-new-formats-test-for-srgb

Fix tex-new-formats to reflect WebGL2 sRGB semantics
Add conformance tests for TEXTURE_BASE_LEVEL and TEXTURE_MAX_LEVEL.
Merge pull request #746 from dvander/mipmap-levels

Add conformance tests for TEXTURE_BASE_LEVEL and TEXTURE_MAX_LEVEL.
Add tests for WebGL2 non-POT texture support.
Exclude WebGL1 npot texture tests in WebGL2.
Merge pull request #743 from dvander/webgl2-non-pot

Add tests for WebGL2 non-POT texture support.
Test basic 3D textures functionality
Add notes on backwards incompatibility in error cases in WebGL 2

As in GLES, behavior in the cases where an earlier API version generates
an error is subject to change in future API versions. Also, in some cases
GLES3.0 can sample a texture even though GLES2.0 would return RGBA =
0, 0, 0, 1.

It seems like a good idea to mention this kind of things in the backwards
incompatibility section for the sake of exhaustiveness, though a complete
list of changed error conditions would seem excessive.
Test basic 3D textures functionality
Merge branch 'test-3d-textures' of github.com:bjacob/WebGL into test-3d-textures

Conflicts:
	sdk/tests/conformance2/core/tex-storage-and-subimage-3d.html
Merge pull request #748 from bjacob/test-3d-textures

Test basic 3D textures functionality
Add tests for miscellaneous parameters.
Merge pull request #747 from dvander/misc-parameters

Add tests for miscellaneous parameters.
Clarify texture access differences in WebGL 2

The only rule that WebGL 2 lifts is that accessing NPOT textures with
certain wrapping or filtering modes should return 0,0,0,1. Other rules
concerning accessing incomplete textures still apply. Make this clear.
Merge pull request #749 from NVIDIA/backwards-incompatibility-errors-note

Add notes on backwards incompatibility in error cases in WebGL 2