Correct sourceMaps option in test and verify it.

Partly fixes #1254

Review URL: https://api.github.com/repos/google/traceur-compiler/issues/1258

Closes #1258, closes #1254.
Hoist function declarations in generator functions

This is so that we do not add a function where it isn't allowed
in ES5 strict mode, due to the CPS transformer.

Fixes #1172
Add support for export default FunctionExpression

and export default ClassExpression

We parse the expression as a FunctionExpression and if it has a name
we change it into a FunctionDeclaration. Same goes for ClassExpression.

Fixes #1208
Define what polyfills to include in the Makefile

The Makefile now lists the polyfills to include. These files register
themselves and then the polyfills.js initializes the polyfills for The
given global.

Fixes #1244