Add the DEBUG macro to accompany LOG, ERROR and WARNING.

data/core/macros/interface-utils.cfg

@@ -443,6 +443,19 @@
     {FADE_STEP 0 5}
 #enddef
 
+#define DEBUG TEXT
+    # Logs a debug message to console. It does nothing unless the 'wml'
+    # log domain is set to debug level at application startup (usually with
+    # --log-debug=wml).
+    #
+    # Example:
+    # ! {DEBUG "inconsistency: $unit.id is not loyal!"}
+    [wml_message]
+        logger=debug
+        message={TEXT}
+    [/wml_message]
+#enddef
+
 #define LOG TEXT
     # Logs a message to console. It does nothing unless the 'wml'
     # log domain is set to log level at application startup (usually with