ash: fix "return N" not setting $? in loop conditionals

ash: fix "return N" not setting $? in loop conditionals

Upstream commit 1:

    Date: Mon, 6 Oct 2014 20:45:04 +0800
    [EVAL] Move common skipcount logic into skiploop

    The functions evalloop and evalfor share the logic on checking
    and updating skipcount.  This patch moves that into the helper
    function skiploop.

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

    Date: Mon, 6 Oct 2014 21:22:43 +0800
    [BUILTIN] Allow return in loop conditional to set exit status

    https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=332954

    When return is used in a loop conditional the exit status will
    be lost because we always set the exit status at the end of the
    loop to that of the last command executed in the body.

    This is counterintuitive and contrary to what most other shells do.

    This patch fixes this by always preserving the exit status of
    return when it is used in a loop conditional.

    The patch was originally written by Gerrit Pape <pape@smarden.org>.

    Reported-by: Stephane Chazelas <stephane_chazelas@yahoo.fr>
    Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>