Snoop option as argument of Trigger.__init__()

Having the "snoop" option as a constructor argument makes more sense, and
avoids having to manuallt set "this.snoop = true" after calling to the
superclass constructor.
Bugzilla: Added "natural language" bug id expander

It is quite simple for the moment, it recognizes patterns like:

 - <name> bug <bugid>
 - <name> bug #<bugid>
Bugzilla: Report invalid bug ids