clearing feedback messages on Ajax upload

[Garret Wilson]

Hi, all. I've done a bit of searching to find the answer, and nothing 
quite seemed to fit, or was obsolete, or was deprecated, or was vague. 
So I'll ask on the list.

I have a page that uses a multipart form submit. It allows the user to 
select a file, and has an AjaxSubmitLink with the label "Go" that 1) 
uploads a large file and then 2) does something that takes a long time. 
When finished, it calls info("finished!") to show a success message in 
the feedback area.

So let's suppose that the user selects a file and selects "Go". After 
the file is uploaded, the processing takes place and the feedback area 
says "finished!" Perfect.

Question: If the user selects /another/ file and selects "Go" /again/, 
how can I immediately remove the "finished!" message, either A) as soon 
as the user selects "Go" or B) as soon as the file finishes uploading 
but before processeing starts? (I greatly prefer option B.)

Thanks,

Garret