[Systems] wrong MIME type on mirrors

[Wade Brainerd]

MIME types served by ASLO are inconsistent.

http://mirrors.ibiblio.org/pub/mirrors/sugar/activities/4193/physics-3.xo
- text/plain
http://mirrors.rit.edu/sugarlabs/activities/4193/physics-3.xo -
application/octet-stream

These were tested using wget.

We should do an audit of all ASLO mirrors to make sure they're using
the correct MIME types for .xo files.  In the ibiblio case, it causes
Safari to display the bundle as plain text.  This is certainly going
to confuse users who are checking out ASLO from non-Sugar systems.

Further, I think we should try and add a warning to the Download link
if the detected browser is not Browse.  It should just say that to use
the file, you need to have Sugar, and provide a link to the Get Sugar
page.

Thanks,
Wade