Promise.coroutine: yielding a function should not call the function

[giltayar]

1. What version of bluebird is the issue happening on?
   3.4.7

2. What platform and version? (For example Node.js 0.12 or Google Chrome 32)
   Tested on Node 7, but I'm guessing it's true for all platforms

3. Did this issue happen with earlier version of bluebird?
   Probably.

Given:

(Promise.coroutine(function*() {
  yield function () { console.log('hi'); };
}))();

You would not expect "hi" to be written to log, because we're yielding a value (which is a function), and not calling the function.

But it does print "hi". And then returns a rejected error.

I have prepared a pull-request that contains a fix, which I will submit in a few minutes.

[benjamingr]

Fix LGTM. @petkaantonov ptal.

[petkaantonov]

+ "" is sufficient

[benjamingr]

Or String(value)

[giltayar]

I chose @benjamingr's change - it seems more explicit to me. Thanks for pointing the (I hope slightly) awkward code out.