Add VectorOfPostprocessors and test ref #4176
Updated Doxygen comments
(refs #4176)
Merge pull request #1 from aeslaughter/vector_of_postprocessors

Updated Doxygen comments
Merge pull request #4177 from bwspenc/vector_of_postprocessors

Add VectorOfPostprocessors and test
Merge commit '4ba2d90cda85f2b030919f8d6bb47b2c021d05e5'