Fix crash on Windows XP.

Fix crash on Windows XP.

The pointer returned by GetEnvironmentStrings() on Unicode versions of
Windows XP was to the raw environment block, not a copy as described in
the documentation.  Retrieving it into service->initial_env and keeping
it around for the lifetime of the service could cause a crash.  Instead
we now copy the memory and immediately call FreeEnvironmentStrings().

Thanks Scott Ware.