Log Message:
Changes 1.8.5.2:
* "git diff -- ':(icase)makefile'" was unnecessarily rejected at the
  command line parser.
* "git cat-file --batch-check=ok" did not check the existence of
  the named object.
* "git am --abort" sometimes complained about not being able to write
  a tree with an 0{40} object in it.
* Two processes creating loose objects at the same time could have
  failed unnecessarily when the name of their new objects started
  with the same byte value, due to a race condition.
Also contains typofixes, documentation updates and trivial code clean-ups