Made some changes to the way that attachments are downloaded -- changed the

Made some changes to the way that attachments are downloaded -- changed the
content-type to "application/octet-stream" so that it will always get downloaded.
If it is an image, it has a "view" button beside it for convenience, and that
will load the picture in the browser.

Updated the configuration script, and documentation on mime

git-svn-id: https://svn.code.sf.net/p/squirrelmail/code/trunk/squirrelmail@574 7612ce4b-ef26-0410-bec9-ea0150e637f0