tests: stabilize test-patch.t on Windows
$PYTHON needs to be quoted when invoking with cmd.exe, because the value expands
to c:/Python27/python.exe, which seems to be interpreted as 'c' being a command.
We can't just convert to '\', because there are a few places that run $PYTHON
directly in MSYS. If unquoted there, it results in c:Python27python.exe being
run. I wonder if we should bake the quotes into the environment variable to
It also wasn't happy with the quoting around exit1.py:
c:/Python27/python.exe: can't open file ''$TESTTMP/d/exit1.py'': [Errno 22] Invalid argument