Fix regression where llHTTPRequests which did not get an OK response returned 499 and the exception message in the http_response event rather than the actual response code and body.

This was a regression since commit 831e4c3 (Thu Apr 4 00:36:15 2013)
This commit also adds a regression test for this case, though this currently only works with Mono
This aims to address http://opensimulator.org/mantis/view.php?id=6704
Merge branch 'master' of ssh://opensimulator.org/var/git/opensim