Fixing login redirect issue

`parse_url` would fail on some relative paths (but not all, interestingly). I originally did it this way to prevent people from linking `http://yoursite.com/login?return=http://badsite.com` and redirecting users away from your site. 

Adding `!parse_url($uri['return'], PHP_URL_SCHEME)` will maintain that security check while allowing 100% of relative URLs to redirect properly in my testing.