Merge branch 'nr/git-cd-to-a-directory'

Just like "make -C <directory>", make "git -C <directory> ..." to
go there before doing anything else.

* nr/git-cd-to-a-directory:
t0056: "git -C" test updates
git: run in a directory given with -C option

diff --cc Documentation/git.txt
Simple merge

diff --cc git.c
Simple merge