ash,hush: set exit code 127 in "sh /does/not/exist" case

ash,hush: set exit code 127 in "sh /does/not/exist" case

Upstream commit 1 for ash:

    [ERROR] Allow the originator of EXERROR to set the exit status

    Some errors have exit status values specified by POSIX and it is
    therefore desirable to be able to set the exit status at the EXERROR
    source rather than in main.c.

    Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Upstream commit 2 for ash:

    [INPUT] Use exit status 127 when the script to run does not exist

    This commit makes dash exit with return code 127 instead of 2 if
    started as non-interactive shell with a non-existent command_file
    specified as argument (or a directory), as documented in
     http://www.opengroup.org/onlinepubs/009695399/utilities/sh.html#tag_04_128_14

    The wrong exit code was reported by Clint Adams and Jari Aalto through
     http://bugs.debian.org/548743
     http://bugs.debian.org/548687

    Signed-off-by: Gerrit Pape <pape@smarden.org>
    Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
NB: in fact, http://bugs.debian.org/548687 was not fixed by this:
"sh /dir/" thinks that EISDIR error on read is EOF, and exits 0.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>