Add STENCIL_BITS and DEPTH_BITS tests to webgl-depth-texture.html

Ensure DEPTH_BITS returns >= 16 bits for UNSIGNED_SHORT and >= 24 bits for UNSIGNED_INT
If there is stencil, ensure STENCIL_BITS reports >= 8 for UNSIGNED_INT_24_8_WEBGL.
Change DEPTH_BITS for UNSIGNED_INT from 24 to 16.

The depth texture extension says the following with regard to UNSIGNED_INT depth textures.
"As per the OpenGL ES spec, there is no guarantee that the OpenGL ES implementation will use the to determine how to store the depth texture internally. It may choose to downsample the 32-bit depth values to 16-bit or even 24-bit."

For the sake of not imposing new requirements, we'll change the minimum depth for UNSIGNED_INT from 24 to 16.
Add DEPTH_BITS and STENCIL_BITS requirements to WEBGL_depth_texture extension

UNSIGNED_SHORT --> Depth: >= 16 Stencil: 0
UNSIGNED_INT --> Depth: >= 16 Stencil: 0
UNSIGNED_INT_24_8_WEBGL --> Depth: >= 24 Stencil: >= 8
Merge branch 'master' of https://github.com/RafaelCintron/WebGL into depthTexture
Merge pull request #670 from RafaelCintron/depthTexture

Add STENCIL_BITS and DEPTH_BITS tests to webgl-depth-texture.html