Merge branch 'jc/maint-blame-no-such-path'

Merge branch 'jc/maint-blame-no-such-path'

"git blame MAKEFILE" run in a history that has "Makefile" but not
"MAKEFILE" should say "No such file MAKEFILE in HEAD", but got
confused on a case insensitive filesystem and failed to do so.

Even during a conflicted merge, "git blame $path" always meant to
blame uncommitted changes to the "working tree" version; make it
more useful by showing cleanly merged parts as coming from the other
branch that is being merged.

* jc/maint-blame-no-such-path:
  blame: allow "blame file" in the middle of a conflicted merge
  blame $path: avoid getting fooled by case insensitive filesystems