Add support of 303 to hostRewrite option

Created by: abanctelchevrel

My backend implements a POST to http://api.domain.com/resources with the following response :

• Status Code : 303 See Other
• Location header : http://api.domain.com/resources/resourceId

I use node-http-proxy (through grunt-proxy) to bypass SOP on my single page app (hosted on localhost:9000), but when I POST on /resources I keep having rejected request because of SOP, even using the hostRewrite option as follows :

httpProxy.createProxyServer({
                ...
                hostRewrite: 'localhost:9000'
              })

Digging into node-http-proxy code I found this test on response code in setRedirectHostRewrite precondition :

var redirectRegex = /^30(1|2|3|7|8)$/;

Why not add 303 to this condition ?