(svn r6788) - Codechange: Add and use a function to test if a string ID is a custom name.

functions.h

@@ -138,6 +138,7 @@ void PlaceTreesRandomly(void);
 void InitializeLandscapeVariables(bool only_constants);
 
 /* misc.c */
+bool IsCustomName(StringID id);
 void DeleteName(StringID id);
 char *GetName(int id, char *buff);