Arkadiusz Drabczyk authored Nov 24, 2019 and Brad King committed Apr 15, 2020

In git, apart from setting username and e-mail in `.gitconfig` it's also
possible to set username in `/etc/passwd` and set e-mail using the
`EMAIL` environment variable.  The advantage of this method is that
other programs such as `mutt` or `doxygen` will pick up these settings
up so there is no need to set them separately in each program.  The
previous way of checking if username and e-mail are set using `git
config` results in failure if they are set using this method.

Instead use `GIT_AUTHOR_IDENT` when `rev` and `cut` tools are available
to parse out the relevant components.

Co-Author: Brad King <brad.king@kitware.com>
Co-Author: Jiri Malak <malak.jiri@gmail.com>