Fix for #147

I've updated the format value functions to allow a 0 value to be bound to inputs. I also updated a test in test-form to cover the case, and re-included this file in test-browser. (I guess you may want to un-include this from test-browser again)

Hopefully this PR includes only the correct files!
No, those tests are valid - and the change I recommended shouldn't affect the behavior of `coerceToString` - ie, `String(value || '')` and `typeof value === 'undefined' || value === null ? '' : String(value)` should be identical.