spawnProcess on win32 should close its self.hProcess handle

New submission from amaury <None>:

In `_dumbwin32proc.Process`, the process handle should be closed when the process has ended, otherwise it's a resource leak.

Also, the `self.hThread` member is still filled, but the handle is always closed. I suggest to close it at the end: `hThread` can be useful is some cases to control the process (I do use it to call `PostThreadMessage` with a `WM_QUIT` message).

The attached patch closes and clears both handles when the process terminates.

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Type     : enhancement
Component: core
Keywords : 
Priority : normal
Nosy     : 
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http://twistedmatrix.com/trac/ticket/3893