Remove extra redirect when automatically dropping sessions and fix issue with ?destination set by other modules.

Problem

Currently the code in session_limit_session_limit will redirect to session_limit_page whenever there is a collision. If the module is configured to automatically drop older sessions it the code to do so is executed and then drupal_goto() is called again redirecting the user too ... the front page. Because it's called w/ no paramaters and any ?destination that was previously set is wiped out by the previous call to drupal_goto() in session_limit_session_limit.

Proposed resolution

Move the code that handles auto dropping of session to session_limit_session_limit. This avoids the problem with loss of ?destination and means there is one less redirect necessary.

To test

You can see this problem in action by installing a module like login_destination and configuring session_limit to allow 1 session and automatically drop others. Then try and view a specific page like node/1 and click a link to login from that page that uses the ?destination paramater to redirect back to that page after login. (The login or signup to post comments link for example). If you're logged in in another browser your session in that browser will be dropped but you'll be redirected to the front page instead of back to node/1.

Attached patch implements the proposed solution.