Kernel: Forked children should inherit their RangeAllocator by copy.

Otherwise we'll start handing out addresses that are very likely already in
use by existing ranges.

Kernel/VM/RangeAllocator.h

@@ -46,6 +46,7 @@ private:
 class RangeAllocator {
 public:
     RangeAllocator(LinearAddress, size_t);
+    RangeAllocator(const RangeAllocator&);
     ~RangeAllocator();
 
     Range allocate_anywhere(size_t);