Fix #364: clash with exporting under org/com/java with Rhino.

The fix is to erase the special values that Rhino puts in the
global scope with undefined values.
Fix #362: Don't call equals when comparing with literal null
Fix #367: Really forbid export of constructors of js.Any
Fix #361: Forbid exporting local classes and objects
Merge pull request #366 from sjrd/fix-364

Fix #364: clash with exporting under org/com/java with Rhino.
Merge pull request #368 from gzm0/bugfixes

Bugfixes