Changed the way we handle HTTP headers internally so that they appear

case-insensitive, but the original case is preserved for output. This increases the chances of working with non-compliant clients without changing the external interface. Fixed #2970.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@6546 bcc190cf-cafb-0310-a4f2-bffc1f526a37