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