Ensure a certain, predictable order of executed events

[jfilak]

It is nice that one can drop a script with a new definition of a known event to the libreport events directory and libreport will run the script along with other scripts for the event, but we need to ensure some unique and predictable order of those scripts. The main reason for doing so is the efficiency of abrtd, the greatest libreport user, where it may execute a "heavy" 'post-create' event followed by a "light-weight" one that discards the former results. In the previous example, the natural and optimal order is reversed.