File upload of .swf file

Issue Summary

Here's a backport of the feature I added to the Drupal 5 upgrade (http://drupal.org/node/133273). It changes the way users supply the .swf file on the block configuration form, from a manually coded path to a file upload.

It was suggested to me that perhaps the textfield should be left in, so that users have the flexibility to either upload or manually enter the path of the .swf. I followed the module of user picture uploads in user.module, but perhaps there's a good argument for allowing flexibility here. Any thoughts?