add a regression test which our current mksh does not pass,

but the one fixed by a diff by jaredy@openbsd (which intro-
duces other problems though):
Log message:
Change the behavior of IFS word-splitting:  split words
when the current character is IFS space and the last
character was a word character or it was non-white IFS
space and the current character is non-white IFS space.
This deviates from the previous behavior because the
latter splits words when the last character is any IFS
space and the current is non-white IFS, resulting in
more fields most of the time.

This new behavior follows what the man page describes;
i.e., that a field is delimited by one or more IFS
whitespace characters followed by zero or one non-white
IFS characters.

tests/ifs.t

@@ -159,3 +159,17 @@ expected-stdout:
 	 <10> <h> <ith> <ere>
 	 <11> <h:ith:ere>
 ---
+
+name: IFS-subst-2
+description:
+	manual page test, IFS=<space>:
+stdin:
+	showargs() { for i; do echo -n " <$i>"; done; echo; }
+	IFS=" :"
+	x=" A :  B::D"
+	echo -n '1:'; for i in $x ; do echo -n " [$i]" ; done ; echo
+	showargs 2 $x
+expected-stdout:
+	1: [A] [B] [] [D]
+	 <2> <A> <B> <> <D>
+---