Teach wmllint to do the safe part of the music namespace changes,

...and document what has already been done.

RELEASE_NOTES

@@ -23,5 +23,16 @@ can read about it here: http://www.wesnoth.org/wiki/Authoring_tools
 Many blocker bugs (yet not officially reported, *tsk*) related to the "update
 add-ons" dialog functionality have been fixed.
 
+The music namespace has been reorganized a bit.  UMC authors should know 
+of the following name changes 
+
+      main_menu.ogg -> transience.ogg, 
+      main_menu_new.ogg -> main_menu.ogg
+      nr-sad.ogg -> sad.ogg
+
+We don't try to handle the first two automatically in wmllint, as it's
+not perfectly clear whether UMC authors want the track or the riole when 
+they name "main_menu.ogg".
+
 ***
 

data/tools/wmllint

@@ -139,6 +139,7 @@ linechanges = (
         ("advanceto=", "advances_to="),
         # This changed after 1.5.5, to enable mechanical spellchecking
         ("sabre", "saber"),
+        ("nr-sad.ogg", "sad.ogg"),
         )
 
 def validate_stack(stack, filename, lineno):