I like to have "private" settings in a git include file, and store the
main .gitconfig under version control. I do not want any authentication
keys or tokens (even if encrypted) in version control, so I have by main
.gitconfig include another file which is local and not tracked.

The current implementation calls `git config --global --get-regexp
<keyPrefix>` and for some reason, this command does not follow git
include files.

The changes suggested in this PR add the `--includes` flag to the
command, which then reads any included files.