Add memory leak unit test for "hook" function flavor.

testing/btest/core/leaks/hook.bro

@@ -0,0 +1,78 @@
+# Needs perftools support.
+#
+# @TEST-GROUP: leaks
+#
+# @TEST-REQUIRES: bro  --help 2>&1 | grep -q mem-leaks
+#
+# @TEST-EXEC: HEAP_CHECK_DUMP_DIRECTORY=. HEAPCHECK=local bro -m -b -r $TRACES/wikipedia.trace %INPUT
+
+type rec: record {
+	a: count;
+	b: string;
+};
+
+global myhook: hook(r: rec);
+global myhook2: hook(s: string);
+# a hook doesn't have to take any arguments
+global myhook4: hook();
+
+hook myhook(r: rec) &priority=5
+	{
+	print "myhook, &priority=5", r;
+	# break statement short-circuits the hook handling chain.
+	break;
+	print "ERROR: break statement should return from hook handler body";
+	}
+
+hook myhook(r: rec)
+	{
+	# This handler shouldn't execute ever because of the handler at priority=5
+	# exiting the body from a "break" statement.
+	print "myhook, &priority=0", rec;
+	}
+
+hook myhook(r: rec) &priority=10
+	{
+	print "myhook, &priority=10", r;
+	# modifications to the record argument will be seen by remaining handlers.
+	r$a = 37;
+	r$b = "goobye world";
+	# returning from the handler early, is fine, remaining handlers still run.
+	return;
+	print "ERROR: break statement should return from hook handler body";
+	}
+
+# hook function doesn't need a declaration, we can go straight to defining
+# a handler body.
+hook myhook3(i: count)
+	{
+	print "myhook3", i;
+	}
+
+hook myhook4() &priority=1
+	{
+	print "myhook4", 1;
+	}
+
+hook myhook4() &priority=2
+	{
+	print "myhook4", 2;
+	}
+
+event new_connection(c: connection)
+	{
+	print "new_connection", c$id;
+
+	hook myhook([$a=1156, $b="hello world"]);
+
+	# A hook with no handlers is fine, it's just a no-op.
+	hook myhook2("nope");
+
+	hook myhook3(8);
+	hook myhook4();
+
+	# A hook can be treated like other data types and doesn't have to be
+	# invoked directly by name.
+	local h = myhook;
+	hook h([$a=2, $b="it works"]);
+	}