added AbstractStoreInputOperator

commit 0afe7e033308a9844ee4985982339d5a0480ae9b
Author: David Yan <david@datatorrent.com>
Date:   Tue Jan 21 18:43:35 2014 -0800

    corrected comment

commit 18a062c2c185fab13f4d75ce1e629a54cb8f12f6
Author: David Yan <david@datatorrent.com>
Date:   Tue Jan 21 18:36:47 2014 -0800

    added AbstractStoreInputOperator