Merge branch 'bw/protocol-v1'

A new mechanism to upgrade the wire protocol in place is proposed
and demonstrated that it works with the older versions of Git
without harming them.

* bw/protocol-v1:
  Documentation: document Extra Parameters
  ssh: introduce a 'simple' ssh variant
  i5700: add interop test for protocol transition
  http: tell server that the client understands v1
  connect: tell server that the client understands v1
  connect: teach client to recognize v1 server response
  upload-pack, receive-pack: introduce protocol version 1
  daemon: recognize hidden request arguments
  protocol: introduce protocol extension mechanisms
  pkt-line: add packet_write function
  connect: in ref advertisement, shallows are last

upload-pack.c

@@ -18,6 +18,7 @@
 #include "parse-options.h"
 #include "argv-array.h"
 #include "prio-queue.h"
+#include "protocol.h"
 
 static const char * const upload_pack_usage[] = {
 	N_("git upload-pack [<options>] <dir>"),
@@ -1066,6 +1067,23 @@ int cmd_main(int argc, const char **argv)
 		die("'%s' does not appear to be a git repository", dir);
 
 	git_config(upload_pack_config, NULL);
-	upload_pack();
+
+	switch (determine_protocol_version_server()) {
+	case protocol_v1:
+		/*
+		 * v1 is just the original protocol with a version string,
+		 * so just fall through after writing the version string.
+		 */
+		if (advertise_refs || !stateless_rpc)
+			packet_write_fmt(1, "version 1\n");
+
+		/* fallthrough */
+	case protocol_v0:
+		upload_pack();
+		break;
+	case protocol_unknown_version:
+		BUG("unknown protocol version");
+	}
+
 	return 0;
 }