Correctly escape a literal colon in an enclosure;

the \: roff escape is an optional line break.

src/lib/libc/stdlib/getopt_long.3

@@ -1,4 +1,4 @@
-.\"	$OpenBSD: getopt_long.3,v 1.16 2010/09/19 22:22:13 jmc Exp $
+.\"	$OpenBSD: getopt_long.3,v 1.17 2011/01/24 01:50:25 schwarze Exp $
 .\"	$NetBSD: getopt_long.3,v 1.11 2002/10/02 10:54:19 wiz Exp $
 .\"
 .\" Copyright (c) 1988, 1991, 1993
@@ -30,7 +30,7 @@
 .\"
 .\"     @(#)getopt.3	8.5 (Berkeley) 4/27/95
 .\"
-.Dd $Mdocdate: September 19 2010 $
+.Dd $Mdocdate: January 24 2011 $
 .Dt GETOPT_LONG 3
 .Os
 .Sh NAME
@@ -199,7 +199,7 @@ these functions return 0 and store
 in the location pointed to by
 .Fa flag .
 These functions return
-.Sq \:
+.Sq \&:
 if there was a missing option argument,
 .Sq \&?
 if the user specified an unknown or ambiguous option, and