Merge branch 'bw/pathspec-match-submodule-boundary'

An v2.12-era regression in pathspec match logic, which made it look
into submodule tree even when it is not desired, has been fixed.

* bw/pathspec-match-submodule-boundary:
pathspec: only match across submodule boundaries when requested

diff --cc builtin/grep.c
Simple merge

diff --cc pathspec.h
Simple merge

diff --cc tree-walk.c
Simple merge