git-fetch, git-branch: Support local --track via a special remote '.'

This patch adds support for a dummy remote '.' to avoid having
to declare a fake remote like

        [remote "local"]
                url = .
                fetch = refs/heads/*:refs/heads/*

Such a builtin remote simplifies the operation of "git-fetch",
which will populate FETCH_HEAD but will not pretend that two
repositories are in use, will not create a thin pack, and will
not perform any useless remapping of names.  The speed
improvement is around 20%, and it should improve more if
"git-fetch" is converted to a builtin.

To this end, git-parse-remote is grown with a new kind of
remote, 'builtin'.  In git-fetch.sh, we treat the builtin remote
specially in that it needs no pack/store operations.  In fact,
doing git-fetch on a builtin remote will simply populate
FETCH_HEAD appropriately.

The patch also improves of the --track/--no-track support,
extending it so that branch.<name>.remote items referring '.'
can be created.  Finally, it fixes a typo in git-checkout.sh.

Signed-off-by: Paolo Bonzini  <bonzini@gnu.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

git-parse-remote.sh

@@ -9,6 +9,9 @@ get_data_source () {
 	*/*)
 		echo ''
 		;;
+	.)
+		echo self
+		;;
 	*)
 		if test "$(git-config --get "remote.$1.url")"
 		then
@@ -31,6 +34,9 @@ get_remote_url () {
 	'')
 		echo "$1"
 		;;
+	self)
+		echo "$1"
+		;;
 	config)
 		git-config --get "remote.$1.url"
 		;;
@@ -57,7 +63,7 @@ get_default_remote () {
 get_remote_default_refs_for_push () {
 	data_source=$(get_data_source "$1")
 	case "$data_source" in
-	'' | branches)
+	'' | branches | self)
 		;; # no default push mapping, just send matching refs.
 	config)
 		git-config --get-all "remote.$1.push" ;;
@@ -163,6 +169,10 @@ get_remote_default_refs_for_fetch () {
 	case "$data_source" in
 	'')
 		echo "HEAD:" ;;
+	self)
+	        canon_refs_list_for_fetch -d "$1" \
+			$(git-for-each-ref --format='%(refname):')
+		;;
 	config)
 		canon_refs_list_for_fetch -d "$1" \
 			$(git-config --get-all "remote.$1.fetch") ;;
@@ -177,7 +187,7 @@ get_remote_default_refs_for_fetch () {
 					}' "$GIT_DIR/remotes/$1")
 		;;
 	*)
-		die "internal error: get-remote-default-ref-for-push $1" ;;
+		die "internal error: get-remote-default-ref-for-fetch $1" ;;
 	esac
 }