Introspection on trace lambdas

[Bike]

Our trace macro works simply by redefining the traced functions. Besides limiting things to global named functions, there is an additional problem: The introspection interface, e.g. function-source-pos, does not know anything about trace lambdas and so behaves as if the function in trace.lisp is what we want to look at. Which it usually isn't.

SBCL does something with encapsulations for this. Another idea would be to make trace functions their own (funcallable) class, which introspection can then look for and take apart.