Pull up following revision(s) (requested by kre in ticket #982):

bin/sh/eval.c: revision 1.157

PR bin/42184 PR bin/52687  (detailing the same bug).

Fix "command not found" handling so that the error message
goes to stderr (after any redirections are applied).

More importantly, in

foo > /tmp/junk

/tmp/junk should be created, before any attempt is made
to execute (the assumed non-existing) "foo".

All this was always true for any command (not found command)
containing a / in its name

foo/bar >/tmp/junk  2>>/tmp/errs

would have created /tmp/junk, then complained (in /tmp/errs)
about foo/bar not being found.  Now that happens for ordinary
commands as well.

The fix (which I found when I saw differences between our
code and FreeBSD's, where, for the benefit of PR 42184,
this has been fixed, sometime in the past 9 years) is
frighteningly simple.  Simply do not short circuit execution
(or print any error) when the initial lookup fails to
find the command - it will fail anyway when we actually
try running it.  The cost is a (seemingly unnecessary,
except that it really is) fork in this case.

This is what I had been planning, but I expected it would
be much more difficult than it turned out....

XXX pullup-8

(martin)