map depth and stencil buffers activation from GLUT to WebGL
map depth and stencil buffers activation from SDL to WebGL
map depth and stencil buffers activation from GLFW to WebGL
add tests for WebGL context attributes (antialiasing, depth, stencil) when they are enabled or disabled
Merge branch 'webgl_context_attributes' of github.com:anlambert/emscripten into incoming
show alerts if antialiasing, depth or stencil are missing in context attributes test
simplify webgl context attributes test harness code a little