Make XMPPConnection.schedule() protected

This method was never intended to be part of the public API. It's also
critical that the given Runnables complete within a reasonable
time frame so that they don't block following ones.

smack-core/src/main/java/org/jivesoftware/smack/Manager.java

@@ -17,6 +17,8 @@
 package org.jivesoftware.smack;
 
 import java.lang.ref.WeakReference;
+import java.util.concurrent.ScheduledFuture;
+import java.util.concurrent.TimeUnit;
 
 public abstract class Manager {
 
@@ -29,4 +31,8 @@ public abstract class Manager {
     protected final XMPPConnection connection() {
         return weakConnection.get();
     }
+
+    protected ScheduledFuture<?> schedule(Runnable command, long delay, TimeUnit unit) {
+        return connection().schedule(command, delay, unit);
+    }
 }

smack-core/src/main/java/org/jivesoftware/smack/XMPPConnection.java

@@ -1275,7 +1275,7 @@ public abstract class XMPPConnection {
         }
     }
 
-    public ScheduledFuture<?> schedule(Runnable command, long delay, TimeUnit unit) {
+    protected ScheduledFuture<?> schedule(Runnable command, long delay, TimeUnit unit) {
         return executorService.schedule(command, delay, unit);
     }
 

smack-extensions/src/main/java/org/jivesoftware/smackx/ping/PingManager.java

@@ -308,7 +308,7 @@ public class PingManager extends Manager {
             int nextPingIn = pingInterval - delta;
             LOGGER.fine("Scheduling ServerPingTask in " + nextPingIn + " seconds (pingInterval="
                             + pingInterval + ", delta=" + delta + ")");
-            nextAutomaticPing = connection().schedule(pingServerRunnable, pingInterval, TimeUnit.SECONDS);
+            nextAutomaticPing = schedule(pingServerRunnable, pingInterval, TimeUnit.SECONDS);
         }
     }