Add com_standalone cvar for at-runtime handling of mods that do not require the original quake3 game data.

code/client/client.h

@@ -409,7 +409,9 @@ int CL_GetPingQueueCount( void );
 
 void CL_ShutdownRef( void );
 void CL_InitRef( void );
+#ifndef STANDALONE
 qboolean CL_CDKeyValidate( const char *key, const char *checksum );
+#endif
 int CL_ServerStatus( char *serverAddress, char *serverStatusString, int maxLen );
 
 qboolean CL_CheckPaused(void);