* add 'flag:unread' as a synonym for 'flag:new OR NOT flag:seen'

- update documentation
  - update test cases
  - some cleanups in the C++-code
  - bump the database version, to trigger the --rebuild warning

src/tests/test-mu-msg.c

@@ -182,7 +182,7 @@ test_mu_msg_03 (void)
 						 "\nLet's write some fünkÿ text\nusing umlauts.\n\nFoo.\n");
 
 		g_assert_cmpuint (mu_msg_get_flags(msg),
-						  ==, 0);
+						  ==, MU_MSG_FLAG_UNREAD);
 
 	
 		mu_msg_unref (msg);