Make propTypes DEFINE_MANY_MERGED
Make submit button default value appear correctly

Fixes #473.
Merge pull request #487 from spicyj/multi-proptypes

Make propTypes DEFINE_MANY_MERGED
Merge pull request #488 from spicyj/gh-473

Make submit button default value appear correctly
Make bin/jsx --version output the React version according to package.json.

Closes #329.