Enhancing VirtualTicketPermissionsPlugin

I did some work on the VirtualTicketPermissionsPlugin.

See ticket #8926 for patch and progress.

Overview of the new features

• in addition to the group_blacklist, in section [virtualticketpermissions], you can also write a group_whitelist setting.
  • only groups on the whitelist will be considered for the TICKET_IS_..._GROUP permissions
  • the blacklist, if also configured, still works
  • both whitelist and blacklist entries can be regular expressions (each list will be regex-compiled once on component init for performance)
• group names can be mixed-case in addition to the already supported all-lower-case; only complete-upper-case stuff, i.e. PERMISSIONS_PROPER, are excluded
• for all of the TICKET_IS_XXX permissions provided by the module, there is now a corresponding TICKET_IS_NOT_XXX negating the test. This permits writing mutually exclusive workflow steps, like this:

  reassign = assigned,accepted,started -> assigned
  reassign.operations = set_owner
  reassign.permissions = TICKET_IS_OWNER_GROUP
  
  takeover = assigned,accepted,started -> assigned
  takeover.operations = set_owner_to_self
  takeover.permissions = TICKET_IS_NOT_OWNER_GROUP
  OUP
  

  A single user will either see reassign (when they share a group with the current owner), or takeover, but never both (unless they are TRAC_ADMIN, which seems to not call down to the plugin at all, unfortunately)