Replace CRM_Core_Error::fatal() with CRM_Utils_System::permissionDenied()

In many places, CRM_Core_Error::fatal() has been used to bail out on a permissions error. We have CRM_Utils_System::permissionDenied() and could use it appropriately.

Motivation

Returning a fatal error to the browser provides a confusing and unprofessional experience for users. A CMS-provided "Access denied" page (eg per drupal_access_denied() or equivalent or CiviCRM-provided fallback) in place of a CiviCRM fatal error page would look a lot more professional and return appropriate HTTP headers (so, prevent caching by proxies / browser, better inform user, better data in webserver logs).

Fatal errors should be indicative of programming errors or (questionably) configuration errors. Having a web crawler hit a disabled profile and trigger a fatal error means there's a lot more noise in CiviCRM's debug log / PHP error logs than there ought to be; this in turn masks identifying real issues under the hood.

Changes required

Alongside replacement of the older calls, we should update permissionDenied() behaviour to match fatal()'s behaviour.

• permissionDenied() would now interrupt program flow, since that is what fatal() does. (Currently calling permissionDenied() before some DB update won't prevent the update from happening.)
• permissionDenied() should accept a text string to inform the user about the permissions failure, as fatal() does currently
• Proposed change to CRM_Core_Permission::checkMenuItem() needs review
• Needs to appropriately bail out of non-HTTP situations? (Eg in BAO, API or drush.)
• All of the above needs tests

Questions

Should we replace a large number of blocks like below with a single line or centralised router check?

{{ if (!CRM_Core_Permission::checkActionPermission('CiviMember', CRM_Core_Action::DELETE))

{ CRM_Utils_System::permissionDenied(ts('You do not have permission to access this page.')); }

}}

CRM/Core/Permission/Base.php contains a couple of "Drupal 6 only" error messages which I suspect are just outdated - it looks like they are implemented for D7?

CRM/Upgrade/Snapshot/V4p2/Price/BAO/Set.php contains a checkPermission() function which I suspect may never get called?