partial merge and full RCS ID sync with oksh

merged:
• new regression tests
• check.pl (tests/th) better tmpfile handling
• exec.c 1.50: POSIX specifies that for an AND/OR list,
  only the last command's exit status matters for "set -e"
• ksh.1 1.147: document the above
• eval.c 1.39: “Make $(< /nonexistent) have the same behaviour
  as $(cat /nonexistent) wrt. errors (do not unwind and do not
  treat this as fatal if set -e is used).”
  ‣ additionally make shf_open() return errno and actually show
    the error message from the system
• regression-39 test: remove the “maybe” marker
  ‣ but decide on correct POSIX behaviour

already been fixed in mksh:
• check.pl (tests/th) exit 1 if tests fail

not merged:
• main.c 1.52: run traps in unwind() before exiting;
  I’m pretty sure this is already working as-should in mksh
• eval.c 1.38: “Commands executed via `foo` or $( bar ) should
  not inherit "set -e" status.” As discussed in IRC, this is
  just plainly WRONG.

eval.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: eval.c,v 1.37 2011/10/11 14:32:43 otto Exp $	*/
+/*	$OpenBSD: eval.c,v 1.39 2013/07/01 17:25:27 jca Exp $	*/
 
 /*-
  * Copyright (c) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010,
@@ -23,7 +23,7 @@
 
 #include "sh.h"
 
-__RCSID("$MirOS: src/bin/mksh/eval.c,v 1.139 2013/05/02 21:59:49 tg Exp $");
+__RCSID("$MirOS: src/bin/mksh/eval.c,v 1.140 2013/07/21 18:36:00 tg Exp $");
 
 /*
  * string expansion
@@ -870,7 +870,12 @@ expand(
 			break;
 
 		case XCOM:
-			if (newlines) {
+			if (x.u.shf == NULL) {
+				/* $(<...) failed */
+				subst_exstat = 1;
+				/* fake EOF */
+				c = EOF;
+			} else if (newlines) {
 				/* spit out saved NLs */
 				c = '\n';
 				--newlines;
@@ -887,7 +892,8 @@ expand(
 			}
 			if (c == EOF) {
 				newlines = 0;
-				shf_close(x.u.shf);
+				if (x.u.shf)
+					shf_close(x.u.shf);
 				if (x.split)
 					subst_exstat = waitlast();
 				type = XBASE;
@@ -1336,7 +1342,8 @@ comsub(Expand *xp, const char *cp, int fn MKSH_A_UNUSED)
 		shf = shf_open(name = evalstr(io->name, DOTILDE), O_RDONLY, 0,
 			SHF_MAPHI|SHF_CLEXEC);
 		if (shf == NULL)
-			errorf("%s: %s %s", name, "can't open", "$() input");
+			warningf(!Flag(FTALKING), "%s: %s %s: %s", name,
+			    "can't open", "$(<...) input", cstrerror(errno));
 	} else if (fn == FUNSUB) {
 		int ofd1;
 		struct temp *tf = NULL;