add HISTORY; shortened version of diff from Ilya A. Kovalenko

ok millert

src/lib/libc/string/strstr.3

@@ -29,9 +29,9 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.\"	$OpenBSD: strstr.3,v 1.9 2007/05/31 19:19:32 jmc Exp $
+.\"	$OpenBSD: strstr.3,v 1.10 2007/09/19 16:06:45 jmc Exp $
 .\"
-.Dd $Mdocdate: May 31 2007 $
+.Dd $Mdocdate: September 19 2007 $
 .Dt STRSTR 3
 .Os
 .Sh NAME
@@ -85,3 +85,8 @@ The
 .Fn strstr
 function conforms to
 .St -ansiC .
+.Sh HISTORY
+The
+.Fn strcasestr
+function first appeared in
+.Ox 3.8 .