Add swf_path field to custom specific directory for the SWF file

Hi Steven,

We needed to tell SWFaddress the path of the directory that is used by the SWF field to fill the "base" parameter in the swfobject function.

Please find attached the diff file.

Notice: the field is "required".
1) Usually you should use the directory of the SWF file.
2) In good practice, you should not put the SWF file in the Drupal root directory.
So, from my point of view, it should be required.

Give feedback.
If this field should not be "required", I would be glad to make the change.

Alexandre