ash: [BUILTIN] Exit without arguments in a trap should use status outside traps

ash: [BUILTIN] Exit without arguments in a trap should use status outside traps

Upstream commit:

    Date:   Mon Oct 6 10:39:47 2014 +0800
    [BUILTIN] Exit without arguments in a trap should use status outside traps

    POSIX now requires that exit without arguments in a trap should
    return the last command status prior to executing traps.  This
    patch implements this behaviour.

    Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>