Explicitly check method correctness before invoking on the subject

Prior to this change, we attempt to invoke the method and handle any
errors as related to the original call.

Unfortunately, this means that if a inner method call is invalid, this
code is used to handle and incorrectly aborts the call instead of
crashing the actor.
Merge pull request #310 from celluloid/safe-method-dispatch

Inner Method errors are handled as related to outer Method call