Change interpretation of '\"' in here documents with substitution

according to SUSv3 and other modern shells (POSIX allows both).
Idea for the patch (add another lex state) from OpenBSD, but the
implementation differs slightly (and is better in quality).

Also add two testcases (/bin/sh passes both, old mksh only one),
and document the change in the manual page. Sync RCS IDs with OBSD.

lex.c

@@ -1,9 +1,9 @@
-/**	$MirOS: src/bin/mksh/lex.c,v 1.8 2005/10/25 19:53:28 tg Exp $ */
-/*	$OpenBSD: lex.c,v 1.36 2005/03/30 17:16:37 deraadt Exp $	*/
+/**	$MirOS: src/bin/mksh/lex.c,v 1.9 2005/11/22 18:36:19 tg Exp $ */
+/*	$OpenBSD: lex.c,v 1.37 2005/09/11 18:02:27 otto Exp $	*/
 
 #include "sh.h"
 
-__RCSID("$MirOS: src/bin/mksh/lex.c,v 1.8 2005/10/25 19:53:28 tg Exp $");
+__RCSID("$MirOS: src/bin/mksh/lex.c,v 1.9 2005/11/22 18:36:19 tg Exp $");
 
 /* Structure to keep track of the lexing state and the various pieces of info
  * needed for each particular state. */
@@ -218,11 +218,16 @@ yylex(int cf)
 			case '\\':
 				c = getsc();
 				switch (c) {
-				case '"': case '\\':
+				case '"':
+					if ((cf & HEREDOC))
+						goto heredocquote;
+					/* FALLTROUGH */
+				case '\\':
 				case '$': case '`':
 					*wp++ = QCHAR, *wp++ = c;
 					break;
 				default:
+heredocquote:
 					Xcheck(ws, wp);
 					if (c) { /* trailing \ is lost */
 						*wp++ = CHAR, *wp++ = '\\';