Other Windows issues

[alphapapa]

https://www.reddit.com/r/emacs/comments/8y49hv/magittodos_show_source_files_todos_and_fixmes_etc/e2lr37n/

In the latest version, testing for the regular expressions pops up a webbrowser on Windows, and the test always fails. This might not be specific to Windows, depending on the help.format setting of git.

An other way to test it would be passing in an invalid parameter, so the test command could be git grep --magit-todos-test-for-pgrep instead of git grep --help. This never starts an external help command and returns the information on stdout.

Also, a check to see if nice is available on the system would be nice (pun..), since it is not available on Windows.

Keep up the great work, this is really useful!