Zabbix

........S. [ZBX-11426] fixed delete procedure for problem and events

With this change, we made the delete for problem and events more
strict. The first change is swapping the calls for deleting events and
problems, so problems will get deleted first.
The second change is to check if an event is associated to a
problem as a problem event OR a recovery event. If one of the
two conditions is true, we do not delete the event for ensuring
data consistency.
The event will eventually be delete when the related problem
record will be removed.

[svn merge -c r74717 ^/branches/3.4]