React 0.12+, Om 0.8+ compatibility

*   Correctly identify React components as not being JS object props
    React components are now plain objects, so (object? x) was including them
    thinking they were something like, #js {:class ""}
*   Adhere to the new pre/post component? conditions. Specifically, mirror this
    fix: https://github.com/swannodette/om/commit/8aa96e2c00bf73cd19f21e7c8c637b3ba697661f