under Cygwin, Git for Windows should be rejected

path_class.t fails because it runs (roughly) `$git->add("/tmp/asdgsdfgasd")`, but Git for Windows, which is accessible and works under cygwin, does not run with the cygwin mappings, and thus cannot see `/tmp`.

The easiest solution here appears to be fail out under Cygwin if `git --version` looks like this: `git version 2.29.2.windows.2`