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

Some major promise packages, such as 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