Introduce HANDLER typedef.
Introduce HANDLER typedef.

pdbartlett/misc-stuff,pdbartlett/misc-stuff,pdbartlett/misc-stuff,pdbartlett/misc-stuff,pdbartlett/misc-stuff,pdbartlett/misc-stuff,pdbartlett/misc-stuff,pdbartlett/misc-stuff,pdbartlett/misc-stuff,pdbartlett/misc-stuff,pdbartlett/misc-stuff,pdbartlett/misc-stuff,pdbartlett/misc-stuff