Beginnings of massive landing of joki changes.

Relevant nsbeta3+ bugs 43309, 44503, 2634, 2504,5981, 24698, 25758, 33577,
36062, 36217, 41191, 41491, 42356, 42829, 43016
r=saari (joki code). also been tested by heikki and bryner

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dom/public/idl/base/Window.idl

@@ -40,6 +40,7 @@ interface Window {
                  attribute  long pageYOffset;
         readonly attribute  long scrollX;
         readonly attribute  long scrollY;
+		readonly attribute  unsigned long length;
 
         void  dump(in wstring str);
         void  alert(/* ... */);