core,log: new 'MSG' log level between 'INFO' and 'WARN'

We're bumping the current "INFO" level messages to the new "MSG"
level, also making the new level the default.

The old "INFO" level will be used to setup an intermediate level of
logging which is not as verbose as "DEBUG" but still provides some
capabilities to analyze the behavior of a modem.

src/main.c

@@ -44,7 +44,7 @@ static MMBaseManager *manager;
 static gboolean
 quit_cb (gpointer user_data)
 {
-    mm_info ("caught signal, shutting down...");
+    mm_msg ("caught signal, shutting down...");
 
     if (manager)
         g_object_set (manager, MM_BASE_MANAGER_CONNECTION, NULL, NULL);
@@ -178,8 +178,8 @@ main (int argc, char *argv[])
     /* Early register all known errors */
     register_dbus_errors ();
 
-    mm_info ("ModemManager (version " MM_DIST_VERSION ") starting in %s bus...",
-             mm_context_get_test_session () ? "session" : "system");
+    mm_msg ("ModemManager (version " MM_DIST_VERSION ") starting in %s bus...",
+            mm_context_get_test_session () ? "session" : "system");
 
     /* Detect runtime charset conversion support */
     mm_modem_charsets_init ();
@@ -250,7 +250,7 @@ main (int argc, char *argv[])
 
     g_bus_unown_name (name_id);
 
-    mm_info ("ModemManager is shut down");
+    mm_msg ("ModemManager is shut down");
 
     mm_log_shutdown ();