conditionaly build the new imagelib on windows. bug 70938. r=bryner sr=cls

makefile.win

@@ -75,6 +75,10 @@ DIRS =                         \
 # the following are associated with the layout engine
   expat                        \
   gfx                          \
+!if defined(USE_IMG2)
+  gfx2                         \
+  modules\libpr0n              \
+!endif
   modules\plugin               \
   uriloader                    \
   htmlparser                   \