Merge branch 'da/user-useconfigonly'

The "user.useConfigOnly" configuration variable can be used to
force the user to always set user.email & user.name configuration
variables, serving as a reminder for those who work on multiple
projects and do not want to put these in their $HOME/.gitconfig.

* da/user-useconfigonly:
ident: add user.useConfigOnly boolean for when ident shouldn't be guessed
fmt_ident: refactor strictness checks

diff --cc Documentation/config.txt
Simple merge

diff --cc ident.c
Simple merge