bin/sh/cd.c: revision 1.54
	bin/sh/cd.c: revision 1.55
	bin/sh/cd.c: revision 1.56

PR standards/59565 - cd "" is now an error, not == cd .

POSIX 2024 requires that cd "" generate an error message,
and fail.

Until now shells (including this one) have typically equated
it to "cd ." as in the distant past, a lookup of "" as a path
name would return the current directory (aka ".").

From now on, we generate an error, as specified.
(For this commit, the error message is kind of pathetic,
but it is at least there - that will be fixed in a
subsequent commit.)


Improve error messages from cd builtin

Have cd indicate (particularly for when CDPATH is in use,
but also in other cases) which path name was attempted
and failed, and why it failed.   For CDPATH uses, when
(if) the cd eventually fails, prefer the first entry in
which the requested destination path is located (when
the chdir() to it fails), or if there is none of those,
the first lookup which failed to determine if the path
exists there or not (ie: not ENOENT).

If the all attempts return ENOENT simply report the arg
given (after "cd -" and "cd a b" processing), as no
one CDPATH entry is more appropriate than any other.

Inspired by PR standards/59565 but not directly related.


PR bin/59602  PWD update failure message from cd fix.
Only complain about being unable to determine the new
directory name after a cd when -e is given (test for
that was forgotten).