[support] Custom form needs "upload in progress" indicator

[Isaac Simon Hodes]

I have a custom form built using the form API. For usability and to
avoid browser timeouts, I need a way to display an "upload in progress"
indicator while large files are being uploaded to the server.

The file upload module has a nice javascript/hidden iframe functionality
that handles this. (It displays a graphic as the file uploads.) However,
this behaviour is only invoked if a user clicks the "attach" button. If
the user clicks submit (without having clicked "attach" beforehand), the
file is uploaded without any indication that the upload is in progress.

Any ideas? Can I add the "attach" button's behaviour to the submit
button?

Or is there a way to use javascript to automatically submit the entire
form after a file has been attached using the "attach" button? (In this
use case there will only be one file uploaded at a time.)

I have also looked into doing file uploades without using the file
upload module. I'd prefer to stick with the core module, but if there
are ideas for other approaches please let me know.

Thanks very much for your help!