pkt-line: add packet_flush_gently()

packet_flush() would die in case of a write error even though for some
callers an error would be acceptable. Add packet_flush_gently() which
writes a pkt-line flush packet like packet_flush() but does not die in
case of an error. The function is used in a subsequent patch.

Signed-off-by: Lars Schneider <larsxschneider@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

pkt-line.c

@@ -91,6 +91,14 @@ void packet_flush(int fd)
 	write_or_die(fd, "0000", 4);
 }
 
+int packet_flush_gently(int fd)
+{
+	packet_trace("0000", 4, 1);
+	if (write_in_full(fd, "0000", 4) == 4)
+		return 0;
+	return error("flush packet write failed");
+}
+
 void packet_buf_flush(struct strbuf *buf)
 {
 	packet_trace("0000", 4, 1);

pkt-line.h

@@ -23,6 +23,7 @@ void packet_flush(int fd);
 void packet_write_fmt(int fd, const char *fmt, ...) __attribute__((format (printf, 2, 3)));
 void packet_buf_flush(struct strbuf *buf);
 void packet_buf_write(struct strbuf *buf, const char *fmt, ...) __attribute__((format (printf, 2, 3)));
+int packet_flush_gently(int fd);
 int packet_write_fmt_gently(int fd, const char *fmt, ...) __attribute__((format (printf, 2, 3)));
 
 /*