Rename PendingModule to LazyInitializedModule, Fixes 421

Review URL: https://github.com/google/traceur-compiler/pull/450

Closes #450.
test import default as a name

Here is a test for #446. It is passing fine, so this can be left out.

Not sure why I was seeing this fail before.

Review URL: https://github.com/google/traceur-compiler/pull/452