Add debug check under GL_ASSERTIONS that the alignment restrictions for vertex attribute stride and offset presented in WebGL section 6.4 are satisfied in user code. See http://www.khronos.org/registry/webgl/specs/latest/1.0/#6.4 .
Also validate size and stride parameters in calls to glVertexAttribPointer.
Merge pull request #1665 from juj/validate_gl_spec_64

Validate gl spec 64