patch: add dry-run alias for compatibility with other implementations.

Other implementations of patch(1), including GNU patch and "svn patch"
have a --dry-run option which does the same as our -C or --check
option.

Add a new alias to make our implementation more compatible.

MFC after:	1 week

usr.bin/patch/patch.1

@@ -21,7 +21,7 @@
 .\"
 .\" $OpenBSD: patch.1,v 1.27 2014/04/15 06:26:54 jmc Exp $
 .\" $FreeBSD$
-.Dd June 12, 2014
+.Dd June 15, 2014
 .Dt PATCH 1
 .Os
 .Sh NAME
@@ -107,7 +107,7 @@ This is equivalent to specifying
 This option is currently the default, unless
 .Fl -posix
 is specified.
-.It Fl C , Fl Fl check
+.It Fl C , Fl Fl check , Fl Fl dry-run
 Checks that the patch would apply cleanly, but does not modify anything.
 .It Fl c , Fl Fl context
 Forces

usr.bin/patch/patch.c

@@ -469,6 +469,7 @@ get_some_switches(void)
 		{"context",		no_argument,		0,	'c'},
 		{"debug",		required_argument,	0,	'x'},
 		{"directory",		required_argument,	0,	'd'},
+		{"dry-run",		no_argument,		0,	'C'},
 		{"ed",			no_argument,		0,	'e'},
 		{"force",		no_argument,		0,	'f'},
 		{"forward",		no_argument,		0,	'N'},