Move author-only tests to xt directory

so they aren't run on installation by users

xt/00_local_perlcritic.t

@@ -0,0 +1,12 @@
+#!/usr/bin/perl
+# 00_local_perlcritic.t - Test file for PBP compliance for SNMP::Info
+# $Id$
+
+use strict;
+use warnings;
+use Test::More;
+
+eval "use Test::Perl::Critic (-severity => 5)";
+plan skip_all => "Test::Perl::Critic required for testing PBP compliance" if $@;
+
+Test::Perl::Critic::all_critic_ok();