SPY-165: Do not cache the selectedKeys.

Motivation
----------
Caching the selected keys may cause issues if the selector is accessed by different
threads, also the loop for the keys is not using the iterator correct.

Modifications
-------------
Make it not cache the keys and also correctly make use of an iterator to loop through
the keys.

Result
------
No stale/cached selected keys and correctly using the iterator should lead to better
stability during failure cases.

Thanks to Brad Svee (@sveesible) for suggesting the fix

Change-Id: If82cdfc810c758a4196415cb709a03ebd72c3d15
Reviewed-on: http://review.couchbase.org/36222
Reviewed-by: Michael Nitschinger <michael.nitschinger@couchbase.com>
Tested-by: Michael Nitschinger <michael.nitschinger@couchbase.com>

src/main/java/net/spy/memcached/MemcachedConnection.java

@@ -66,7 +66,6 @@
 import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
-import java.util.Set;
 import java.util.SortedMap;
 import java.util.TreeMap;
 import java.util.concurrent.ConcurrentLinkedQueue;
@@ -405,19 +404,21 @@ public void handleIO() throws IOException {
     getLogger().debug("Selecting with delay of %sms", delay);
     assert selectorsMakeSense() : "Selectors don't make sense.";
     int selected = selector.select(delay);
-    Set<SelectionKey> selectedKeys = selector.selectedKeys();
+    //Set<SelectionKey> selectedKeys = selector.selectedKeys();
 
-    if (selectedKeys.isEmpty() && !shutDown) {
+    if (selector.selectedKeys().isEmpty() && !shutDown) {
       handleEmptySelects();
     } else {
       getLogger().debug("Selected %d, selected %d keys", selected,
-        selectedKeys.size());
+        selector.selectedKeys().size());
       emptySelects = 0;
 
-      for (SelectionKey sk : selectedKeys) {
+      Iterator<SelectionKey> iterator = selector.selectedKeys().iterator();
+      while(iterator.hasNext()) {
+        SelectionKey sk = iterator.next();
         handleIO(sk);
+        iterator.remove();
       }
-      selectedKeys.clear();
     }
 
     handleOperationalTasks();