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
  ...

refs.c

@@ -13,6 +13,7 @@
 #include "tag.h"
 #include "submodule.h"
 #include "worktree.h"
+#include "argv-array.h"
 
 /*
  * List of all available backends
@@ -501,6 +502,19 @@ int refname_match(const char *abbrev_name, const char *full_name)
 	return 0;
 }
 
+/*
+ * Given a 'prefix' expand it by the rules in 'ref_rev_parse_rules' and add
+ * the results to 'prefixes'
+ */
+void expand_ref_prefix(struct argv_array *prefixes, const char *prefix)
+{
+	const char **p;
+	int len = strlen(prefix);
+
+	for (p = ref_rev_parse_rules; *p; p++)
+		argv_array_pushf(prefixes, *p, len, prefix);
+}
+
 /*
  * *string and *len will only be substituted, and *string returned (for
  * later free()ing) if the string passed in is a magic short-hand form