[Caja] Fix build under Java 5

[mikesamuel]

Reviewers: metaweta,

Description:
Fix some warnings and the usual problems with JDK1.5 disallowing
@Override annotations on methods that implement interface method.

Please review this at http://codereview.appspot.com/96098

Affected files:
  M     src/com/google/caja/parser/js/CajoledModuleExpression.java
  M     tests/com/google/caja/parser/quasiliteral/CajitaRewriterTest.java