Merge branch 'jk/grep-binary-attribute'

* jk/grep-binary-attribute: grep: pre-load userdiff drivers when threaded grep: load file data after checking binary-ness grep: respect diff attributes for binary-ness grep: cache userdiff_driver in grep_source grep: drop grep_buffer's "name" parameter convert git-grep to use grep_source interface grep: refactor the concept of "grep source" into an object grep: move sha1-reading mutex into low-level code grep: make locking flag global