Don't quote the path to Python unless the path contains an embedded space.

Quoting the path doesn't work on Win2K (cmd.exe) regardless, this is just
a hack to let the test pass again on Win2K (so long as Python isn't
installed in a path that does contain an embedded space).  On Win2K it
looks like we'd also have to add a second pair of double quotes, around
the entire command line.