Merge branch 'bw/protocol-v2'

The beginning of the next-gen transfer protocol.

* bw/protocol-v2: (35 commits)
  remote-curl: don't request v2 when pushing
  remote-curl: implement stateless-connect command
  http: eliminate "# service" line when using protocol v2
  http: don't always add Git-Protocol header
  http: allow providing extra headers for http requests
  remote-curl: store the protocol version the server responded with
  remote-curl: create copy of the service name
  pkt-line: add packet_buf_write_len function
  transport-helper: introduce stateless-connect
  transport-helper: refactor process_connect_service
  transport-helper: remove name parameter
  connect: don't request v2 when pushing
  connect: refactor git_connect to only get the protocol version once
  fetch-pack: support shallow requests
  fetch-pack: perform a fetch using v2
  upload-pack: introduce fetch server command
  push: pass ref prefixes when pushing
  fetch: pass ref prefixes when fetching
  ls-remote: pass ref prefixes when requesting a remote's refs
  transport: convert transport_get_remote_refs to take a list of ref prefixes
  ...

fetch-pack.h

@@ -3,6 +3,7 @@
 
 #include "string-list.h"
 #include "run-command.h"
+#include "protocol.h"
 #include "list-objects-filter-options.h"
 
 struct oid_array;
@@ -53,7 +54,8 @@ struct ref *fetch_pack(struct fetch_pack_args *args,
 		       struct ref **sought,
 		       int nr_sought,
 		       struct oid_array *shallow,
-		       char **pack_lockfile);
+		       char **pack_lockfile,
+		       enum protocol_version version);
 
 /*
  * Print an appropriate error message for each sought ref that wasn't