Merge branch 'rs/grep-no-recursive'

Unlike "grep", "git grep" by default recurses to the whole tree.
The command learned "git grep --recursive" option, so that "git
grep --no-recursive" can serve as a synonym to setting the
max-depth to 0.

* rs/grep-no-recursive:
  grep: add -r/--[no-]recursive

diff --cc builtin/grep.c
Simple merge