[Zeek-Dev] support for event handlers using a subset of parameters

[Vern Paxson]

>     global my_event: event(a: count, b: string);
> 
>     event my_event(b: string)
>         { print "my_event", b; }
> 
> Which is good because:
> 
> * user doesn't care about parameter 'a', so they shouldn't have to list it
> * it makes it easier for to deprecate/change event parameters

This seems like a pretty niche pair of benefits.  Is there a compelling
use-case that's motivating this change?

One thing I initially wondered was whether this was going to tie our hands
in the future if we want to introduce C++-style overloading.  However, it
looks like you've implemented this based on matching the names in the
declaration rather than the types, so that should be okay.

		Vern