Sync to traceur-compiler master
Fix exception in getOwnPropertyDescriptor.
Symptom: Exception in pica calls to getOwnPropertyDescriptor.
Analysis: While getting the property descriptor in the
proxy handler we copy the descriptor of the original object onto
the shadow object, and return the result. This fails because the
shadow object already has a descriptor with different values. That
in turn is caused by a previous call to defineProperty() where we
are given {value: function(){...}}. The only workaround is to disable
a check in reflect.js, see https://github.com/tvcutsem/harmony-reflect/issues/25
Fix: disable a check in reflect.js