How should packages handle installation of scripts that use the #!
mechanism of invoking a shell.  In particular, how should packages
deal with installing perl scripts that begin

     #! /usr/local/bin/perl

Is there a general mechanism for switching this to 

     #! /usr/pkg/bin/perl

or whatever is appropriate for the ${PREFIX}?  Do we have to do manual
patching in each case?  How do you solve this problem?

Cheers,
Brook