Test for va_arg support on struct types (disabled on nested struct)

va_arg is not yet supported on nested struct types (see
https://code.google.com/p/nativeclient/issues/detail?id=3815)
[tracing] Add task tracing.
[tracing] Context data is used on the server side now.
[tracing] Add a way to track "associated storage size".

The docs cover this in more detail.
Fixed emscripten::val handle for special js values (undefined,null,true,false)
[embind docs] Reformat and cleanup whitespace.
val::equals, val::strictlyEquals
Implement _mm_loadu_ps and _mm_storeu_ps
Merge pull request #2929 from waywardmonkeys/embind-docs

[embind docs] Reformat and cleanup whitespace.
Merge pull request #2928 from waywardmonkeys/trace-extensions

Trace extensions
use system libs args processing in precompiled headers
option to use zlib from ports
[trace] Fix copy/paste error.
Implement SDL_SetClipRect/SDL_GetClipRect
Merge pull request #2931 from caiiiycuk/sdl_setcliprect

Implement SDL_SetClipRect/SDL_GetClipRect
Merge pull request #2935 from waywardmonkeys/trace-fix

[trace] Fix copy/paste error.
Only replace slashes if the argument is defined

Fixes #2920
Merge pull request #2936 from aidanhs/aphs-fix-nodejs-no-args

Fix 'require' for emscripten modules in nodejs
fix up test_require
experimental option to emit JSON in EMCC_DEBUG=2 interim phases