Mention the word "regexp" and the fact that this inteface is obsolete

in the NAME section.

Previously, "man -k regex" printed the following two lines
with no hint that you needed to do "man 3 regexp" to get to
the man page associated with the first of the two lines:

regcomp, regexec, regsub, regerror (3) - regular expression handlers
regex, regcomp, regexec, regerror, regfree (3) - regular-expression library

lib/libcompat/regexp/regexp.3

@@ -26,7 +26,7 @@
 .\" SUCH DAMAGE.
 .\"
 .\"     from: @(#)regexp.3	8.1 (Berkeley) 6/4/93
-.\"	$NetBSD: regexp.3,v 1.15 2003/08/07 16:44:17 agc Exp $
+.\"	$NetBSD: regexp.3,v 1.16 2008/09/08 22:14:11 apb Exp $
 .\"
 .Dd June 4, 1993
 .Dt REGEXP 3
@@ -36,7 +36,7 @@
 .Nm regexec ,
 .Nm regsub ,
 .Nm regerror
-.Nd regular expression handlers
+.Nd obsolete "'regexp'" regular expression handlers
 .Sh LIBRARY
 .Lb libcompat
 .Sh SYNOPSIS