Merge branch 'db/clone-in-c'

* db/clone-in-c:
  Add test for cloning with "--reference" repo being a subset of source repo
  Add a test for another combination of --reference
  Test that --reference actually suppresses fetching referenced objects
  clone: fall back to copying if hardlinking fails
  builtin-clone.c: Need to closedir() in copy_or_link_directory()
  builtin-clone: fix initial checkout
  Build in clone
  Provide API access to init_db()
  Add a function to set a non-default work tree
  Allow for having for_each_ref() list extra refs
  Have a constant extern refspec for "--tags"
  Add a library function to add an alternate to the alternates file
  Add a lockfile function to append to a file
  Mark the list of refs to fetch as const

Conflicts:

	cache.h
	t/t5700-clone-reference.sh

Makefile

@@ -235,7 +235,6 @@ BASIC_LDFLAGS =
 
 SCRIPT_SH += git-am.sh
 SCRIPT_SH += git-bisect.sh
-SCRIPT_SH += git-clone.sh
 SCRIPT_SH += git-filter-branch.sh
 SCRIPT_SH += git-lost-found.sh
 SCRIPT_SH += git-merge-octopus.sh
@@ -484,6 +483,7 @@ BUILTIN_OBJS += builtin-check-ref-format.o
 BUILTIN_OBJS += builtin-checkout-index.o
 BUILTIN_OBJS += builtin-checkout.o
 BUILTIN_OBJS += builtin-clean.o
+BUILTIN_OBJS += builtin-clone.o
 BUILTIN_OBJS += builtin-commit-tree.o
 BUILTIN_OBJS += builtin-commit.o
 BUILTIN_OBJS += builtin-config.o