prevent PHP from magically setting a 302 header

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | yes (for people relying on getting a magic 302 when setting a Location header)
| Deprecations? | no
| Tests pass?   | see travis
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

this needs a test case .. but first let me know if you are ok with this change.
see http://www.php.net/manual/en/function.header.php