Merge branch 'ak/format-patch-odir-config'

"git format-patch" learned to notice format.outputDirectory
configuration variable.  This allows "-o <dir>" option to be
omitted on the command line if you always use the same directory in
your workflow.

* ak/format-patch-odir-config:
format-patch: introduce format.outputDirectory configuration

diff --cc Documentation/config.txt
Simple merge

diff --cc Documentation/git-format-patch.txt
Simple merge