pgstat EXEC_BACKEND

For application to HEAD, following community review.

Corrects a typo, introduces missing variables, and rearranges the
initialization of stats process under EXEC_BACKEND. 

[A cleaner, rationalized approach to stat/backend/SSDataBase child processes
under EXEC_BACKEND is on my TODO list. However this patch takes care of
immediate concerns (ie. stats test now passes under win32)]

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