Merge branch 'rs/xdiff-lose-emit-func'

Simplifies the interface between the implementation of "blame" and underlying xdiff engine, and removes a lot of unused or unnecessary code from the latter. By René Scharfe (6) and Ramsay Jones (1) * rs/xdiff-lose-emit-func: builtin/blame.c: Fix a "Using plain integer as NULL pointer" warning xdiff: remove unused functions xdiff: remove emit_func() and xdi_diff_hunks() blame: factor out helper for calling xdi_diff() blame: use hunk_func(), part 2 blame: use hunk_func(), part 1 xdiff: add hunk_func()