Update joomla.sql

Fix default value for the parameter guest_usergroup. This fix could be treated as security fix - if site has wrong value for the guest usergroup (13) and site already has the usergroup with such ID with administrator permissions - all of them would be administrators.
Update joomla.sql

Fix incorrect default value for guest_usergroup for PostgreSQL
Update joomla.sql

Fix incorrect default value for guest_usergroup for SQL Server
Merge pull request #2776 from SergeyLitvinov/patch-1

Fix default value for the parameter guest_usergroup for com_user in joomla.sql