Hardware coloring for itemstacks

Adds the possibility to colorize item stacks based on their metadata.

In the item/node definition you can specify palette (an image file)
and color (fallback color if the item has no palette or metadata).
Then you can add palette_index to the metadata.

Dropped itemstacks with different colors do not merge.

src/script/lua_api/l_metadata.h

@@ -67,6 +67,9 @@ protected:
 
 	// from_table(self, table)
 	static int l_from_table(lua_State *L);
+
+	// equals(self, other)
+	static int l_equals(lua_State *L);
 };
 
 #endif /* L_NODEMETA_H_ */