Merge branch 'cc/receive-pack-limit'

An incoming "git push" that attempts to push too many bytes can now
be rejected by setting a new configuration variable at the receiving
end.

* cc/receive-pack-limit:
  receive-pack: allow a maximum input size to be specified
  unpack-objects: add --max-input-size=<size> option
  index-pack: add --max-input-size=<size> option