comctl32: Implement LVS_EX_DOUBLEBUFFER

[Felix Nawothnig]

Tested with utorrent - completly removes the flickering from #7344.
In case you're wondering about the change in EraseBkgnd() - this is how 
native behaves, they recreate the double buffer on each refresh so we 
need to move the erase. Please tell me if I broke anything.
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  dlls/comctl32/listview.c |   47 
++++++++++++++++++++++++++++++++++++++++++---
  1 files changed, 43 insertions(+), 4 deletions(-)
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