Fix '\%o' for printf from coreutils

The printf utility provided by coreutils when interpreting '\%o' format
does not recognize %o as formatting directive. For example
printf '\%o 0 returns \%o and warning: ignoring excess arguments,
starting with ‘0’, which results in failed tests in
t5309-pack-delta-cycles.sh. In most shells the test ends with success as
the printf is a builtin utility.

Fix it by using '\\%o' which is interpreted consistently in all versions
of printf.
Signed-off-by: NKacper Kornet <draenog@pld-linux.org>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

t/lib-pack.sh

@@ -12,10 +12,10 @@
 # Print the big-endian 4-byte octal representation of $1
 uint32_octal () {
 	n=$1
-	printf '\%o' $(($n / 16777216)); n=$((n % 16777216))
-	printf '\%o' $(($n /    65536)); n=$((n %    65536))
-	printf '\%o' $(($n /      256)); n=$((n %      256))
-	printf '\%o' $(($n           ));
+	printf '\\%o' $(($n / 16777216)); n=$((n % 16777216))
+	printf '\\%o' $(($n /    65536)); n=$((n %    65536))
+	printf '\\%o' $(($n /      256)); n=$((n %      256))
+	printf '\\%o' $(($n           ));
 }
 
 # Print the big-endian 4-byte binary representation of $1