Move "get_ack()" to common git_connect functions

git-clone-pack will want it too. Soon.

connect.c

@@ -1,6 +1,25 @@
 #include "cache.h"
+#include "pkt-line.h"
 #include <sys/wait.h>
 
+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 (!strncmp(line, "ACK ", 3)) {
+		if (!get_sha1_hex(line+4, result_sha1))
+			return 1;
+	}
+	die("git-fetch_pack: expected ACK/NAK, got '%s'", line);
+}
+
 int path_match(const char *path, int nr, char **match)
 {
 	int i;