Send HTTP 302 instead of 307

We are speking HTTP/1.0, so 307 doesn't exist

Signed-off-by: Etienne CHAMPETIER <etienne.champetier@free.fr>

This can sometimes cause problem:
http://dev.wifidog.org/ticket/848

Also 307 mean if i was doing a POST, do a POST on the new location (the splash)
What we really want is 303, but it's HTTP/1.1
see also http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10.3.3