Support for PropTypes.symbol

[bholloway]

I am used to the react PropTypes and I used them for things other than components.

I am using proptypes but now I need to validate for Symbol. This is not in the ~14 code base that is your current implementation.

Do you have any guidance?

[developit]

We'll need to diff against 15.3's proptypes implementation, shouldn't be too difficult.

[liqwid]

I also need a symbol implementation

[developit]

If anyone has time, the implementation just needs to be lifted from the react 15.x source. Big thanks if you can!