Selectively display debug and backtrace information depending on user permissions

During a code meeting we discussed the limitation of the current global debug and backtrace options. The problem is that it can only be turned on or off for the entire site, meaning regular users get the info when they don't want or need it because their site admin turned it on to provide a better bug report.

We determined that

• the global option should remain.
• A new CiviCRM permission should be created called "Show debug and backtrace messages"
• In Drupal 7, administrators will get this permission by default
• Only users with this permission will see the global option and be able to turn it globally on or off
• If on, only users with this permission will see the debug and backtrace information.