Merge branch 'mt/grep-cquote-path'

"git grep" did not quote a path with unusual character like other
commands (like "git diff", "git status") do, but did quote when run
from a subdirectory, both of which has been corrected.

* mt/grep-cquote-path:
  grep: follow conventions for printing paths w/ unusual chars

diff --cc Documentation/git-grep.txt
Simple merge