Improve detection of bad arguments errors in dispatcher handlers.

Improve detection of bad arguments errors in dispatcher handlers.

The previos scheme was based on parsing TypeError messages, so it was very
poor because spourious errors could have been raised (is a subcall inside
a handler made a wrong function call). The new scheme involves a wrapper
with a dummy function with the same signature as the original handler.
The wrapper then call the dummy function to check the arguments and catches
any TypeError in that NOP call. If an error is catched, it's translated to
a WrongArgumentError, if not, the real hanlder is called with that (now
knonw to be right) arguments.

Testcases were updated and extended too.