Subject: bug#22345: consider upgrade to PCRE2

From: Jim Meyering <[email-masked]>
Date: Mon, 11 Jan 2016 16:25:14 +0800

This report of heap overrun in libpcre,
https://bugs.exim.org/show_bug.cgi?id=1767 makes me more inclined to
upgrade grep to use PCRE2, but not before the grep-2.23 release.