add a testcase as documentation (why POSIX isn’t everything); fix comments

check.t

@@ -1,4 +1,4 @@
-# $MirOS: src/bin/mksh/check.t,v 1.741 2016/07/25 00:04:37 tg Exp $
+# $MirOS: src/bin/mksh/check.t,v 1.742 2016/07/25 20:36:24 tg Exp $
 # -*- mode: sh -*-
 #-
 # Copyright © 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010,
@@ -359,6 +359,18 @@ stdin:
 expected-stdout:
 	20
 ---
+name: arith-prec-1
+description:
+	Prove arithmetic expressions with embedded parameter
+	substitutions cannot be parsed ahead of time
+stdin:
+	a='3 + 4'
+	print 1 $((2 * a)) .
+	print 2 $((2 * $a)) .
+expected-stdout:
+	1 14 .
+	2 10 .
+---
 name: arith-div-assoc-1
 description:
 	Check associativity of division operator

main.c

@@ -34,7 +34,7 @@
 #include <locale.h>
 #endif
 
-__RCSID("$MirOS: src/bin/mksh/main.c,v 1.312 2016/07/25 00:04:45 tg Exp $");
+__RCSID("$MirOS: src/bin/mksh/main.c,v 1.313 2016/07/25 20:36:27 tg Exp $");
 
 extern char **environ;
 
@@ -317,7 +317,7 @@ main_init(int argc, const char *argv[], Source **sp, struct block **lp)
 #endif
 		/*
 		 * this is uniform across all OSes unless it
-		 * breaks somewhere; don't try to optimise,
+		 * breaks somewhere hard; don't try to optimise,
 		 * e.g. add stuff for Interix or remove /usr
 		 * for HURD, because e.g. Debian GNU/HURD is
 		 * "keeping a regular /usr"; this is supposed

misc.c

@@ -30,7 +30,7 @@
 #include <grp.h>
 #endif
 
-__RCSID("$MirOS: src/bin/mksh/misc.c,v 1.243 2016/07/25 00:04:45 tg Exp $");
+__RCSID("$MirOS: src/bin/mksh/misc.c,v 1.244 2016/07/25 20:36:28 tg Exp $");
 
 #define KSH_CHVT_FLAG
 #ifdef MKSH_SMALL
@@ -354,7 +354,7 @@ change_xtrace(unsigned char newval, bool dosnapshot)
  */
 int
 parse_args(const char **argv,
-    /* OF_CMDLINE or OF_SET */
+    /* OF_FIRSTTIME, OF_CMDLINE, or OF_SET */
     int what,
     bool *setargsp)
 {