Improve test runner to periodically yield back to browser in Emscripten builds to not hang the browser while running the tests.
Fix Clang 3.3 build issue in Emscripten with SSE1 where float4 - __m128 is not recognized (even when float4 has implicit ctor from __m128).
Remove build warnings for Emscripten with SSE1.
Fix MATH_SSE1 build to more strictly only access SSE1 and not leak in SSE2 constructs.
Fix Emscripten Clang 3.3 float4->__m128 cast issue.
Fix build warning.
Make Emscripten debug builds do a _very_ minimal amount of iterations because of SAFE_HEAP=1 being very slow.