The destination string is declared as "s" but referred to as "dst"

in some cases.  Be consistent and use "dst" everywhere like for
strlcat(3) and strncat(3).  From Tim Kuijsten.

src/lib/libc/string/strcat.3

@@ -1,4 +1,4 @@
-.\"	$OpenBSD: strcat.3,v 1.17 2014/04/19 11:30:40 deraadt Exp $
+.\"	$OpenBSD: strcat.3,v 1.18 2016/05/26 21:30:13 millert Exp $
 .\"
 .\" Copyright (c) 1990, 1991 The Regents of the University of California.
 .\" All rights reserved.
@@ -31,7 +31,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd $Mdocdate: April 19 2014 $
+.Dd $Mdocdate: May 26 2016 $
 .Dt STRCAT 3
 .Os
 .Sh NAME
@@ -40,14 +40,14 @@
 .Sh SYNOPSIS
 .In string.h
 .Ft char *
-.Fn strcat "char *s" "const char *append"
+.Fn strcat "char *dst" "const char *append"
 .Sh DESCRIPTION
 The
 .Fn strcat
 function appends a copy of the NUL-terminated string
 .Fa append
 to the end of the NUL-terminated string
-.Fa s ,
+.Fa dst ,
 then adds a terminating
 .Ql \e0 .
 .Pp
@@ -60,7 +60,7 @@ subsequent memory will be damaged.
 The
 .Fn strcat
 function return the pointer
-.Fa s .
+.Fa dst .
 .Sh SEE ALSO
 .Xr strlcpy 3 ,
 .Xr wcscat 3 ,