Merge branch 'jc/alternate-push'

* jc/alternate-push:
  push: receiver end advertises refs from alternate repositories
  push: prepare sender to receive extended ref information from the receiver
  receive-pack: make it a builtin
  is_directory(): a generic helper function

diff --cc Makefile
Simple merge

diff --cc builtin-clone.c
Simple merge

diff --cc builtin-fetch-pack.c
Simple merge

diff --cc builtin-send-pack.c
Simple merge

diff --cc builtin.h
Simple merge

diff --cc daemon.c
Simple merge

diff --cc git.c
Simple merge

diff --cc sha1_file.c
Simple merge