Report an error on circular dependencies.

Add a test for circular dependency.
Detect and report useful error message:
"Unsupported circular dependency between feature/Modules/ImportCircular.module
and feature/Modules/resources/clockwise"
See issue #684.

Review URL: https://api.github.com/repos/google/traceur-compiler/issues/728

Closes #728.
Add test for duplicate calls to ModuleStore.registerModule()
Throw on duplicate calls to ModuleStore.registerModule