hush: output bash-compat killing signal names

This significantly syncronises ash-signals and hush-signals tests.

function                                             old     new   delta
process_wait_result                                  449     450      +1

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

shell/ash_test/ash-signals/usage.tests

@@ -0,0 +1,23 @@
+# no output -- default state
+echo ___
+trap
+
+# assign some traps
+echo ___
+trap "a" EXIT INT USR1 USR2
+
+# show them all
+echo ___
+trap
+
+# clear one
+echo ___
+trap 0 INT
+echo ___
+trap
+
+# clear another
+echo ___
+trap "-" USR1
+echo ___
+trap