music: Rename phase 2 music links.

Doom 2 music lumps have random names and I can never remember them.
It's useful to be able to browse the musics/ directory and know
which track goes which which level. Rename links to the consistent
format d_mapxy.mus and do the naming translation inside the config
file.

buildcfg.txt

@@ -521,40 +521,38 @@ D_DM2INT
 
 #ifndef FREEDM
 
-D_RUNNIN
-D_STALKS
-D_COUNTD
-D_BETWEE
-D_DOOM
-D_THE_DA
-D_SHAWN
-D_DDTBLU
-D_IN_CIT
-D_DEAD
-D_STLKS2
-D_THEDA2
-D_DOOM2
-D_DDTBL2
-D_RUNNI2
-D_DEAD2
-D_STLKS3
-D_ROMERO
-D_SHAWN2
-D_MESSAG
-D_COUNT2
-D_DDTBL3
-D_AMPIE
-D_THEDA3
-D_ADRIAN
-D_MESSG2
-D_ROMER2
-D_TENSE
-D_SHAWN3
-D_OPENIN
-D_EVIL
-D_ULTIMA
-D_READ_M
-D_DM2TTL
+D_RUNNIN = D_MAP01
+D_STALKS = D_MAP02
+D_COUNTD = D_MAP03
+D_BETWEE = D_MAP04
+D_DOOM   = D_MAP05
+D_THE_DA = D_MAP06
+D_SHAWN  = D_MAP07
+D_DDTBLU = D_MAP08
+D_IN_CIT = D_MAP09
+D_DEAD   = D_MAP10
+D_STLKS2 = D_MAP11
+D_THEDA2 = D_MAP12
+D_DOOM2  = D_MAP13
+D_DDTBL2 = D_MAP14
+D_RUNNI2 = D_MAP15
+D_DEAD2  = D_MAP16
+D_STLKS3 = D_MAP17
+D_ROMERO = D_MAP18
+D_SHAWN2 = D_MAP19
+D_MESSAG = D_MAP20
+D_COUNT2 = D_MAP21
+D_DDTBL3 = D_MAP22
+D_AMPIE  = D_MAP23
+D_THEDA3 = D_MAP24
+D_ADRIAN = D_MAP25
+D_MESSG2 = D_MAP26
+D_ROMER2 = D_MAP27
+D_TENSE  = D_MAP28
+D_SHAWN3 = D_MAP29
+D_OPENIN = D_MAP30
+D_EVIL   = D_MAP31
+D_ULTIMA = D_MAP32
 
 #else /* FREEDM */