Bug 981218 - Remove the JSAutoCompartment from cx pushing. r=bobowen

By this point, AutoJSAPI takes care of entering the correct compartment, so this
no longer serves a purpose.
Bug 981218 - Stop using default compartment objects in nsJSUtils.cpp. r=bobowen
Bug 981218 - Stop using default compartment objects in workers. r=bobowen
Bug 981218 - Remove default compartment object usage in js shell and tests. r=luke
Bug 981218 - Stop using a default compartment object in the IndexedDB and ProxyAutoConfig JSRuntimes. r=bobowen
Bug 981218 - Remove default compartment objects. r=luke

\o/