Perl libraries. If there is no Perl around, it will be built first,
anyway, and the Makefile will be re-sourced afterwards.
(Thanks to Krister Walfridsson for this)
Fix the Perl interface of nnrpd for Perl 5.8: The #includes for
embedded Perl use a hardcoded "my_perl" for the interpreter instance
variable. Rename variable in lib/perl.c accordingly, make it globally
visible and declare it extern in nnrpd/perl.c. "Now I can post again."
Todo: Check Perl 5.6 compatibility.