Logging: log using the log var names directly.

Currently we have to log by writing something like:

  static log_var_t log_a_b_c = LOG_VAR_INIT("a.b.c");
  log (log_a_b_c, "msg");

This is sort of annoying.  Let's just write:

  log("a.b.c", "msg");

test/unit/log.c

@@ -176,8 +176,7 @@ TEST_END
  */
 TEST_BEGIN(test_log_only_format_string) {
 	if (false) {
-		static log_var_t l = LOG_VAR_INIT("str");
-		log(l, "No arguments follow this format string.");
+		log("log_str", "No arguments follow this format string.");
 	}
 }
 TEST_END