Enhancement: should print out stacktrace of caught exceptions in debug mode.

[gergely-ujvari]

I suggest a very simple, yet (IMHO) very helpful suggestions. I was using jschannel for notification and the function which it've called had an obvious error in it, but jschannel quietly ate the exception, even in debug mode, and the only error it gave back is a "runtime_error" string, which is far from being helpful.

After inspecting the code, I think adding a simple console.log(e.stack) or something similar (only in debug mode) here: https://github.com/mozilla/jschannel/blob/master/src/jschannel.js#L390
would help a great deal when debugging.