Merge branch 'jt/format-patch-from-config'

"git format-patch" learned format.from configuration variable to
specify the default settings for its "--from" option.

* jt/format-patch-from-config:
format-patch: format.from gives the default for --from

diff --cc Documentation/config.txt
Simple merge

diff --cc builtin/log.c
Simple merge

diff --cc contrib/completion/git-completion.bash
Simple merge

diff --cc t/t4014-format-patch.sh
Simple merge