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.right

@@ -0,0 +1,14 @@
+___
+___
+___
+trap -- 'a' EXIT
+trap -- 'a' INT
+trap -- 'a' USR1
+trap -- 'a' USR2
+___
+___
+trap -- 'a' USR1
+trap -- 'a' USR2
+___
+___
+trap -- 'a' USR2