Nathan Shively-Sanders ae652404cd Fix JSX attribute checking when spreading unions
Previously, the code didn't account for the fact that spreading a union
creates a union. In fact, before Decemeber, spreading a union in JSX
didn't create a union.

Now the check for properties of the spread type uses
`getPropertiesOfType`, which works with unions, instead of accessing the
`properties` property directly.
2018-01-22 13:34:12 -08:00
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