[imp] Allow setting of Http status code in com_redirect

This feature allows the setting of the Http status code in com_redirect. This has many SEO related benefits as you may well wish to redirect with a non-301 code (a 501 or something crazy like that even).

It also gives much greater flexability to the redirect method in JApplication in order to do this. As that only allowed a redirect with a 301 or 303.

As this is an advanced option and should only be used by those who actually know what their doing I've dumped it in an advanced options parameter for the component. I've also built it in such a way that we can add more things into the advanced section in the future if we want. If the user has this turned off (which he will by default) then they will continue to redirect with a 301