Writable slaves expires: fix leak in key tracking.

We need to use a dictionary type that frees the key, since we copy the
keys in the dictionary we use to track expires created in the slave
side.

src/expire.c

@@ -315,8 +315,17 @@ void expireSlaveKeys(void) {
 /* Track keys that received an EXPIRE or similar command in the context
  * of a writable slave. */
 void rememberSlaveKeyWithExpire(redisDb *db, robj *key) {
-    if (slaveKeysWithExpire == NULL)
-        slaveKeysWithExpire = dictCreate(&keyptrDictType,NULL);
+    if (slaveKeysWithExpire == NULL) {
+        static dictType dt = {
+            dictSdsHash,                /* hash function */
+            NULL,                       /* key dup */
+            NULL,                       /* val dup */
+            dictSdsKeyCompare,          /* key compare */
+            dictSdsDestructor,          /* key destructor */
+            NULL                        /* val destructor */
+        };
+        slaveKeysWithExpire = dictCreate(&dt,NULL);
+    }
     if (db->id > 63) return;
 
     dictEntry *de = dictAddOrFind(slaveKeysWithExpire,key->ptr);

src/server.h

@@ -1742,6 +1742,11 @@ void evictionPoolAlloc(void);
 unsigned long LFUGetTimeInMinutes(void);
 uint8_t LFULogIncr(uint8_t value);
 
+/* Keys hashing / comparison functions for dict.c hash tables. */
+unsigned int dictSdsHash(const void *key);
+int dictSdsKeyCompare(void *privdata, const void *key1, const void *key2);
+void dictSdsDestructor(void *privdata, void *val);
+
 /* Git SHA1 */
 char *redisGitSHA1(void);
 char *redisGitDirty(void);