Move "get_ack()" back to fetch-pack

In 41cb7488 Linus moved this function to connect.c for reuse inside
of the git-clone-pack command.  That was 2005, but in 2006 Junio
retired git-clone-pack in commit efc7fa53.  Since then the only
caller has been fetch-pack.  Since this ACK/NAK exchange is only
used by the fetch-pack/upload-pack protocol we should move it back
to be a private detail of fetch-pack.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/builtin-fetch-pack.c b/builtin-fetch-pack.c
index 783c2b0..7c09d46 100644
--- a/builtin-fetch-pack.c
+++ b/builtin-fetch-pack.c
@@ -157,6 +157,27 @@
 	return commit->object.sha1;
 }
 
+static int get_ack(int fd, unsigned char *result_sha1)
+{
+	static char line[1000];
+	int len = packet_read_line(fd, line, sizeof(line));
+
+	if (!len)
+		die("git fetch-pack: expected ACK/NAK, got EOF");
+	if (line[len-1] == '\n')
+		line[--len] = 0;
+	if (!strcmp(line, "NAK"))
+		return 0;
+	if (!prefixcmp(line, "ACK ")) {
+		if (!get_sha1_hex(line+4, result_sha1)) {
+			if (strstr(line+45, "continue"))
+				return 2;
+			return 1;
+		}
+	}
+	die("git fetch_pack: expected ACK/NAK, got '%s'", line);
+}
+
 static int find_common(int fd[2], unsigned char *result_sha1,
 		       struct ref *refs)
 {