purl_goto should use a 301 redirect

After some internal issue and discussion I believe purl_goto() should use a 301 redirect by default.

301 is a permanent redirect
302 is a temporary redirect

If purl_goto()'s purpose is to redirect to the "correct" URL, It should use a 301 redirect. I can't think of a use case where PURL would be set up to use a temporary redirect. However this is just changing the default behavior and the redirect type can still be passed in.