Doing rethrow right in python
Fixing bugs and improving exception handling mechanism.

-Properly inserting the catch variable in the locals or env (case the
 try/catch is in a closure)

-Throwing a MemetalkException on parse error.

-Showing parse error messages in the idez UI (Closes #40).

-Trying to workaround the invalid state of proc.evaluator (which messes
 with the next instructions to be executed) when executing a try block
 that raises an exception by using a separate Eval object.
-tests/eval1.mm working again (missing `instantiate` method)

Also cleaned up tests working with CompiledFunction.