Experimentally try full-size LLLeap stream test on Windows.

The new toolchain may (!) have fixed a longstanding bug in LLLeap / APR when
we try to pump large volumes of data through a Windows named pipe using APR
nonblocking I/O. This used to fail pretty consistently because the APR
nonblocking write call would sometimes spuriously return "would block" when in
fact the data buffer was completely written; the caller would later retry,
which of course would duplicate some of the data in the pipe. Preliminary
experiments with VS 2013 suggest this may have been resolved. This changeset
is to propagate the experiment to a wider range of Windows systems; we may
need to revert it if in fact the bug persists.