Closes #656. Add a getNumActive() method to JedisPool to provide access to the current state of the internal pool.

src/test/java/redis/clients/jedis/tests/JedisPoolTest.java

@@ -238,4 +238,35 @@ public class JedisPoolTest extends Assert {
 	pool.returnResource(null);
 	pool.returnResourceObject(null);
     }
+
+    @Test
+    public void getNumActiveIsNegativeWhenPoolIsClosed() {
+        JedisPool pool = new JedisPool(new JedisPoolConfig(), hnp.getHost(),
+                hnp.getPort(), 2000, "foobared", 0, "my_shiny_client_name");
+
+        pool.destroy();
+        assertTrue(pool.getNumActive() < 0);
+    }
+
+    @Test
+    public void getNumActiveReturnsTheCorrectNumber() {
+        JedisPool pool = new JedisPool(new JedisPoolConfig(), hnp.getHost(),
+            hnp.getPort(), 2000);
+        Jedis jedis = pool.getResource();
+        jedis.auth("foobared");
+        jedis.set("foo", "bar");
+        assertEquals("bar", jedis.get("foo"));
+
+        assertEquals(1, pool.getNumActive());
+
+        Jedis jedis2 = pool.getResource();
+        jedis.auth("foobared");
+        jedis.set("foo", "bar");
+
+        assertEquals(2, pool.getNumActive());
+
+        pool.returnResource(jedis);
+        pool.returnResource(jedis2);
+        pool.destroy();
+    }
 }