New primitive engine, bugfixes: take 3

- new primitive emulation engine based on BoxesRunTime - no more hardcoded methods
- fix bug causing module to be reinitialized when usage goes in and out of scope - module in heap looked up by its symbol instead of by value
- add primitive and exception tests
Sure thing. Names are path-dependent, so they need to be recreated when they need to be passed across universe boundaries. It's okay.