Squashed commit of the following:

commit 8ad1e5d6665b790af4dcec432062860fc1863153
Author: Siyuan Hua <siyuan@datatorrent.com>
Date:   Fri Sep 26 13:20:18 2014 -0700

    SPOI-3244 #resolve #comment fix the ConcurrentModificationException

commit e890a19030024e6a82e915690dfe5076a8e77459
Author: Siyuan Hua <siyuan@datatorrent.com>
Date:   Wed Sep 24 15:25:58 2014 -0700

    bug fix

commit 2c9fbb18c8f2440668ca922915f2488b4a8cfcb2
Author: Siyuan Hua <siyuan@datatorrent.com>
Date:   Wed Sep 24 15:18:32 2014 -0700

    bug fix

commit 197e32071d76f70e01adc173edfe4454f1fd8c5a
Author: Siyuan Hua <siyuan@datatorrent.com>
Date:   Wed Sep 24 13:51:59 2014 -0700

    Use sticky key

commit 5fe00d2732b2ca2c020ba4990875f6bfc1264f92
Author: Siyuan Hua <siyuan@datatorrent.com>
Date:   Wed Sep 24 12:40:25 2014 -0700

    Add throughput control to kafka output application