(svn r1503) Added feature:

o allows users to setup the production values of the rawmaterial producing 
  industries in the editor

Modified:
o ttd.h - added CT_INVALID for 0xFF cargo type
o english.txt - added 1 string
o industry_gui.c - the feature itself
o window.h - added compile asserts to the structs which checks whether their
  sizes are smaller than WINDOW_CUSTOM_SIZE

Thanks:
o Darkvater to bother me to constantly improve the patch
o Various users at #openttd for testing

ttd.h

@@ -268,6 +268,8 @@ enum {
 	CT_FIZZY_DRINKS = 11,
 
 	NUM_CARGO = 12,
+
+	CT_INVALID = 0xFF
 };
 
 typedef uint AcceptedCargo[NUM_CARGO];