memcached: bump to version 1.4.21

And add hash file.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/memcached/memcached.hash

@@ -0,0 +1,2 @@
+# From http://www.memcached.org/files/memcached-1.4.21.tar.gz.sha1
+sha1	ab10c46dd9f5d4401872d9670e575afa5bc7d66f	memcached-1.4.21.tar.gz

package/memcached/memcached.mk

@@ -4,7 +4,7 @@
 #
 ################################################################################
 
-MEMCACHED_VERSION = 1.4.20
+MEMCACHED_VERSION = 1.4.21
 MEMCACHED_SITE = http://www.memcached.org/files
 MEMCACHED_DEPENDENCIES = libevent
 MEMCACHED_CONF_ENV = ac_cv_prog_cc_c99='-std=gnu99'