Add validation to avoid creating views with same path defined for page display

I ran into a problem after creating 2 views with the same path, and discovering the page view only worked for one of them. I believe it is the same problem discussed in this issue: http://drupal.org/node/278651

Since that issue is set to "won't fix", perhaps a validation could be added to the code that would warn the user in the event they try to save a path that is already in use by another view.