Patch that creates the enhancement
The current software only allows redirects with 301 and 302 (and does not even document that, ts). This patch adds also the possibility to create 303 redirects. This is required so that extensions can be compatibel to W3C standards on resource representation serving, as described in Web Architecture http://www.w3.org/TR/webarch/ and especially TAG issue 14 on httpRange http://www.w3.org/2001/tag/issues.html#httpRange-14
The patch also allows to set the response code on redirects to 303. It could be extended for even more redirect codes, but this seems not required yet (I searched the bugzilla list).