Add call needles except for inheritance. Make "callers:" searches work. Fix bug 930911. Fix bug 1082102.

* Modify compiler plugin to emit everything we need. No more concrete call graph needed on the Python side.
* Remove called-by filter. It's stupid and useless.
* "callers:" queries now find actual callsites, not just the functions containing callsites!
* Restore some genexprs that had turned into list comps for debugging.
* Remove callee tests, since we're getting rid of called-by search.

To come: making the rest of the test_callers tests pass