under Cygwin, Git for Windows should be rejected

[wchristian]

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