Add test for program-level handlers.

In its own test file rather than catch.t, so as not to cause trouble
debugging issues with catch.t tests.

Author: jnthn

S04-exception-handlers/top-level.t

@@ -0,0 +1,14 @@
+use v6;
+
+use Test;
+
+plan 1;
+
+sub foo { die };
+foo;
+
+CATCH {
+    when * {
+        pass 'Top-level handler caught exception'
+    }
+}