Original URL request parameters are lost when going through log in screen

I have a plug-in that looks for a certain request parameter when a user starts a new discussion. I link to a URL like /post/discussion?test=1 to activate this plugin's behaviour.

If the user is not logged in, they are first sent to the sign in page at /entry/signin?Target=post%2Fdiscussion , and after signing in they reach /post/discussion, with the "test" parameter lost.

This pull request fixes this.