gives possibility to use ref property for Creatable

[blacktemplar]

fixes issue #1644

[coveralls]

Coverage decreased (-0.1%) to 92.611% when pulling 08ed387 on blacktemplar:ref-prop-in-creatable into a0e5855 on JedWatson:master.

[gwyneplaine]

thanks for this @blacktemplar this has been merged into master.

[aaronincincy]

This appears to be causing warnings for me (react-select@1.1.0, react@15.6.2). I'm using ref={r=>this.selector = r} and getting:

Warning: CreatableSelect: ref is not a prop. Trying to access it will result in undefined being returned. If you need to access the same value within the child component, you should pass it as a different prop. (https://fb.me/react-special-props)

I believe this is because ref is reserved, so you can't really pass it through like you are. If you renamed it to selectRef for Creatable (and updated the documentation for this exception to the Select API) I believe that would solve the issue.

My code seems to still work ok (it was working before upgrading from rc10), but I'd like to get rid of the warning if possible.