Patch for making session-memcache-db.inc work if memcache is not installed

The following patch allows the session-memcache-db.inc file to still work, and defer to db, if memcache is not actually running.

Index: sites/all/modules/memcache/session-memcache-db.inc
===================================================================
--- sites/all/modules/memcache/session-memcache-db.inc	(revision 429)
+++ sites/all/modules/memcache/session-memcache-db.inc	(working copy)
@@ -29,7 +29,8 @@
   }
 
   // If user session is in memcache, use it, otherwise load from db.
-  $user = dmemcache_get($key, 'session');
+  if(function_exists('dmemcache_get'))
+    $user = dmemcache_get($key, 'session');
   if(!$user) {
   	$user = db_fetch_object(db_query("SELECT u.*, s.* FROM {users} u INNER JOIN {sessions} s ON u.uid = s.uid WHERE s.sid = '%s'", $key));
   }