Merge commit '6f02181'

Merge commit '6f02181'

* commit '6f02181':
  helpers: separately determine if stdout and stderr are ttys.
  cmd/newliner: restrict progress lines to the screen width.
  hashsplit: use shorter offset-filenames inside trees.
  Replace 040000 and 0100644 constants with GIT_MODE_{TREE,FILE}
  git.py: rename treeparse to tree_decode() and add tree_encode().
  hashsplit.py: remove PackWriter-specific knowledge.
  cmd/split: fixup progress message, and print -b output incrementally.
  hashsplit.py: convert from 'bits' to 'level' earlier in the sequence.
  hashsplit.py: okay, *really* fix BLOB_MAX.
  hashsplit.py: simplify code and fix BLOB_MAX handling.
  options.py: o.fatal(): print error after, not before, usage message.
  options.py: make --usage just print the usage message.