[ZPT] Compilation errors

[Richard Jones]

If a template fails compilation and an attempt is made to render it, the 
exception raised is a RuntimeError. I think this should be changed to 
something that is a little more unique to ZPT, so I can catch the exception 
an not worry about catching stray RuntimeErrors raised by faults in e.g. the 
Python interpreter (I don't beileve anything else raises RuntimeErrors.) 
Sure, use RuntimeError as a base class, but maybe PTRuntimeError at a minimum?

Yes/No/Indifferent?


   Richard