tools: parse pre-release node.js version numbers

`node` binaries built from upstream git have a "-pre" suffix attached
to the version number.  Fix the version parser to handle those.
change getTexUnitType assertion to warnOnce
Merge branch 'fixup-node-version-check' of github.com:bnoordhuis/emscripten into incoming

Conflicts:
	AUTHORS
Adds to a test case verifying glGetIntegerv returns
correct results when the current texture id is not TEXTURE0 and fixes
library_gl.js so that it returns correct results.
Merge branch 'incoming' of https://github.com/kripken/emscripten into new-beta2
Merge branch 'glgetintegerv-fix' into new-beta2

* glgetintegerv-fix:
  Adds to a test case verifying glGetIntegerv returns correct results when the current texture id is not TEXTURE0 and fixes library_gl.js so that it returns correct results.