Items displayed in Attachments macro can cause system instability

The attachment macro currently calls a viewfile macro on each item that is a xls,xlsx, and pdf.

On a page that pulls in many attachments, or on pages with lots of attachment macros, you can end up in a situation where you denial of service yourself (run out of threads in http pool) or cause you to run out of memory (due to lots of requests for view file at the same time).

The macro should either limit, or there ought to be a flag to disable this behavior.