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>

shell/ash_test/ash-misc/exitcode_trap1.right

@@ -0,0 +1,2 @@
+Trapped
+One:1

shell/ash_test/ash-misc/exitcode_trap1.tests

@@ -0,0 +1,6 @@
+# "exit" in trap should not use last command's exitcode,
+# but exitcode on entering the trap.
+(trap "echo Trapped; exit" EXIT
+ (exit 1)
+)
+echo One:$?