The form validate does not need to be called until we are done processin...

The form validate does not need to be called until we are done processing all of the images; this fixes the multiple image fields on the node creating multiple nodes bug; still need to handle multiple images within an image field.
@chrisschaub The call to _image_field_form_process() is async, so I don't think it is safe to proceed with the form_validation() until  the  _image_field_form_process()'s success callback is called on the final image field.

Proceeding with the form validation (AFAIK) will cause the form to be submitted (AKA node POST) before the image(s) have been uploaded, and the file id(s) won't get attached to the node's field(s) properly.