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>