Any solution to this can be a problem, you can't just ignore everything after the ?
Imagine a blog post with this URL: myblog.com/?post=152
Many websites depend on what follows after the ? to display different content, even hubski a few months ago used to do that.
But I agree that a method to compare URL similarities is a good idea. I think this method should warn the user about previous posts or give them a list of similar URLs, ultimately the user will have to make the decision of posting that URL based on manual comparison with the list of similar URLs.