Fixed #4148 -- Changed the way attachments are served to IE to avoid some

      caching and header-related bugs there. Only comes into play when Internet
Explorer is the user-agent.

Patch from Michael Axiak, with testing from Axis_of_Entropy and Karen Tracey.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@7856 bcc190cf-cafb-0310-a4f2-bffc1f526a37