Validation fixes

I'd recommend viewing each commit on its own, since the diffs are clearer and explanations are in the extended commit message :-)
See the commit message for this change (https://github.com/mozilla/treeherder-ui/commit/0641672139704187a5a779017f5fa71cd3594ecf). The page linked from there says that the http-equiv statements are ignored by most browsers and we should be using HTTP headers (ie tweak our apache config).