Convert existing die(..., strerror(errno)) to die_errno()

Change calls to die(..., strerror(errno)) to use the new die_errno().

In the process, also make slight style adjustments: at least state
_something_ about the function that failed (instead of just printing
the pathname), and put paths in single quotes.

Signed-off-by: Thomas Rast <trast@student.ethz.ch>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/refs.c b/refs.c
index 24438c6..dffe395 100644
--- a/refs.c
+++ b/refs.c
@@ -1418,7 +1418,7 @@
 	logfile = git_path("logs/%s", ref);
 	logfd = open(logfile, O_RDONLY, 0);
 	if (logfd < 0)
-		die("Unable to read log %s: %s", logfile, strerror(errno));
+		die_errno("Unable to read log '%s'", logfile);
 	fstat(logfd, &st);
 	if (!st.st_size)
 		die("Log %s is empty.", logfile);