Add DocString to clarify the purpose of 'is_non_posix_and_non_windows_os'.
Add DocString to clarify the purpose of 'is_non_posix_and_non_windows_os'.

* subversion/tests/cmdline/prop_tests.py
  (is_non_posix_and_non_windows_os): Add DocString.

Suggested by: dlr

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion