Bug 845862 - Transitively apply waivers for accessor descriptors. r=mrbkap
Bug 843829 - Fix incorrect test. r=mrbkap

This wasn't actually testing anything, because |is| is defined in the scope of
the content, so by passing the objects as arguments, we end up re-wrapping them
in the content scope, where the distinction between waived and non-waived
objects doesn't exist.

We're actually just about to remove this test in the next patch, but I wanted
to make it correct first. :-)
Bug 843829 - Apply transitive waivers for nativeCall. r=mrbkap
Bug 843829 - Stop using IsTransparent for XBL field access, and explicitly waive instead. r=mrbkap
Bug 843829 - Explicitly add a waiver in FieldGetter and FieldSetter. r=mrbkap
Bug 843829 - Wrap unwaived content JS objects in opaque wrappers for XBL scopes. r=mrbkap