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 $PYTHON directly in MSYS. If unquoted there, it results in c:Python27python.exe being run. I wonder if we should bake the quotes into the environment variable to avoid this. It also wasn't happy with the quoting around exit1.py: c:/Python27/python.exe: can't open file ''$TESTTMP/d/exit1.py'': [Errno 22] Invalid argument