hush: implement "return NUM in trap sets $? after trap"

function                                             old     new   delta
builtin_return                                        47      67     +20
check_and_run_traps                                  243     259     +16
run_pipe                                            1583    1597     +14
hush_main                                           1076    1086     +10
run_list                                            1054    1055      +1
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 5/0 up/down: 61/0)               Total: 61 bytes

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

shell/hush_test/hush-misc/exitcode_trap3.right

@@ -0,0 +1,2 @@
+TERM
+42:42

shell/hush_test/hush-misc/exitcode_trap3.tests

@@ -0,0 +1,9 @@
+# "return" in trap should not use last command's exitcode,
+# but exitcode on entering the trap.
+trap "echo TERM;return" term
+f() {
+	(sleep 1; kill $$) &
+	until (exit 42) do (exit 42); done
+}
+f
+echo 42:$?

shell/hush_test/hush-misc/exitcode_trap4.right

@@ -0,0 +1,2 @@
+TERM
+11:11

shell/hush_test/hush-misc/exitcode_trap4.tests

@@ -0,0 +1,8 @@
+# "return" in trap sets $? after trap
+trap "echo TERM;return 11" term
+f() {
+	(sleep 1; kill $$) &
+	until (exit 42) do (exit 42); done
+}
+f
+echo 11:$?

shell/hush_test/hush-misc/exitcode_trap5.right

@@ -0,0 +1,3 @@
+TERM
+Nested
+Zero:0

shell/hush_test/hush-misc/exitcode_trap5.tests

@@ -0,0 +1,10 @@
+# "return" in trap sets $? after trap...
+# ...but not a nested one!
+g() { echo Nested; return 22; }
+trap "echo TERM;false;g" term
+f() {
+	(kill $$) &
+	sleep 1
+}
+f
+echo Zero:$?