End `Bacon.fromPromise()` handler chains with `.done()` if present.

Some major promise packages, such as
[kriskowal/q](https://github.com/kriskowal/q) will silently eat
exceptions happening in a promise handlers unless the promise chain is
ended with `.done()`. This patch ensures `Bacon.fromPromise` ends such
promise chains. See
https://github.com/kriskowal/q/wiki/Coming-from-jQuery#exception-handling
Fixes #501