cg-push protocol proposal

I'd like to propose the following protocol for 'pushes'. Assume that a 'git-daemon' is the 'server', and is talking on stdin/stdout.

Each command is an ascii string, followed by a LF (\n)

Request current head ID:

	  head <head-name>\n

	Responses:

	  head <head-name> <sha1>\n

	  error <head-name> <hex-code> <error-string>\n

Request a SHA1 blob from the server

	  send <sha1>\n

	Responses:

	  send <sha1> <hex-size>\n<bytes...>

	  error <sha1> <hex-code> <error-string>\n

Update head ID to a SHA1 (the SHA1 may already be in the server's DB)

	  head <head-name> <old-sha1> <sha1>\n

1)	Response if <head-name> is now <sha1>:

	  head <head-name> <sha1>\n

	Response if error, or head locked by someone else updating:

	  error <head-name> <hex-code> <error-string>\n

	Response if <sha1> is not in the database:

	  send <sha1>\n		- Server needs the blob

2)	Client response if 'send' is returned:
 
	  send <sha1> <hex-size>\n<bytes...>

3)	Response if more objects are needed 
          (ie you sent a commit or tree object)

	  send <new-sha1>\n	- Server needs blob

	  Remember the SHA1 you sent, 'call' step 2) with new-sha1 
	  Goto 3)

	Response if send succeeded:

	  exists <sha1>\n

	Response if send failed:

	  error <sha1> <hex-code> <error-string>\n

TODO: Tags