Re-support type="text/traceur" to enable global semantics for scripts

...tics for scripts

	Fixes #822

	The difference between scripts with type="module" and "text/traceur" is that the "text/traceur" script's globals will be global to all the other scripts, just like regular es5 script tags.

Review URL: https://api.github.com/repos/google/traceur-compiler/issues/1033

Closes #1033, closes #822.