add RES_UNIQUE, required for sound code

This was SVN commit r1209.

source/lib/res/h_mgr.cpp

@@ -505,7 +505,7 @@ Handle h_alloc(H_Type type, const char* fn, uint flags, ...)
 	if(!key)
 		flags |= RES_NO_CACHE;	// changes scope to RES_TEMP
 	// check if already loaded (cached)
-	else
+	else if(!(flags & RES_UNIQUE))
 	{
 		// object already loaded?
 		h = h_find(type, key);

source/lib/res/h_mgr.h

@@ -160,6 +160,9 @@ enum
 	// alias for RES_TEMP scope. the handle will not be kept open.
 	RES_NO_CACHE = 1,
 
+	// not cached, and will never reuse a previous instance
+	RES_UNIQUE = 1|16,
+
 	// the resource isn't backed by a file. the fn parameter is treated as the search key (uintptr_t)
 	// currently only used by mem manager
 	RES_KEY = 8