Fixed glSampleCoverage signature (vi to vii)

The signature for glSampleCoverage was incorrect (vi); glSampleCoverage takes two arguments (vii).

See: https://www.khronos.org/registry/webgl/specs/1.0.2/#5.14.3
and http://www.khronos.org/opengles/sdk/docs/man/xhtml/glSampleCoverage.xml
[SDL Audio] Refactoring Mix_LoadWAV_RW to use new FS API.

The old API was causing issues with certain file systems, as the `read` property required the execute bit AND the read bit to be set before it would return `true`.

As a side benefit, the new code is simpler and cleaner.
Merge pull request #1891 from onnoj/incoming

Fixed glSampleCoverage signature (vi to vii)
do not assume fastcomp emits 'pre' table
finalize function table masks for fastcomp
handle global initializers from fastcomp
shorten test_cubescript for fastcomp now that it passes
fix memset return value in makeSetValues
Merge pull request #1894 from jvilk/legacy_fs_remove

[SDL Audio] Refactoring Mix_LoadWAV_RW to use new FS API.
Merge branch 'incoming' of https://github.com/kripken/emscripten into new-beta2