[Toybox] Applied the expr.c patch.

[Rob Landley]

But the main reason expr is still in pending is:

$ expr 4 \* 3 / 2
6
$ ./toybox expr 4 \* 3 / 2
4

I.E. some operators have equal precedence, it's not a strictly ordered list.

And yes, the posix spec is broken. The "extended description" section
talks about horizontal lines separating operators of equal precedence,
but there aren't any horizontal lines in the HTML table. It looks like
something that got eaten by a formatting change and nobody ever noticed.
(It's there in the 2008 release _and_ still there in 2013. I pinged the
austin group mailing list that maintains the spec...)

Rob