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>

shell.c

@@ -60,7 +60,7 @@ int main(int argc, char **argv)
 	while (devnull_fd >= 0 && devnull_fd <= 2)
 		devnull_fd = dup(devnull_fd);
 	if (devnull_fd == -1)
-		die("opening /dev/null failed (%s)", strerror(errno));
+		die_errno("opening /dev/null failed");
 	close (devnull_fd);
 
 	/*