Merge branch 'mt/grep-submodule-textconv'

"git grep --recurse-submodules" takes trees and blobs from the
submodule repository, but the textconv settings when processing a
blob from the submodule is not taken from the submodule repository.
A test is added to demonstrate the issue, without fixing it.

* mt/grep-submodule-textconv:
  grep: demonstrate bug with textconv attributes and submodules

diff --cc grep.h
Simple merge