Add Music_BatchExempt, temporarily exemplify a tune from batch operations

src/music.cpp

@@ -353,3 +353,13 @@ const char* Music_CurrentId(void)
 {
 	return g_tunes.current_id();
 }
+
+void Music_BatchExempt(const char* id)
+{
+	Tune* tune = g_tunes.find(id);
+
+	if (tune)
+	{
+		tune->resist_once = true;
+	}
+}

src/music.h

@@ -92,6 +92,10 @@ void Music_Remap(const char *id, const char *song);
 // Set whether a tune should loop.
 void Music_Loop(const char *id, boolean loop);
 
+// Temporarily exemplify a tune from batch operations, such
+// as Music_StopAll.
+void Music_BatchExempt(const char *id);
+
 
 //
 // Query properties.

src/music_manager.hpp

@@ -73,6 +73,12 @@ public:
 	{
 		for (auto& [_, tune] : map_)
 		{
+			if (tune.resist_once)
+			{
+				tune.resist_once = false;
+				continue;
+			}
+
 			if (!tune.resist)
 			{
 				f(tune);

src/music_tune.hpp

@@ -57,6 +57,7 @@ public:
 	// from TuneManager::stop_all etc. It must be
 	// stopped/paused individually.
 	bool resist = false;
+	bool resist_once = false; // set at runtime
 
 	// This tune shows a credit when first played (not
 	// resumed).