stagnant models from bugs volume 2
Merge branch 'develop' of https://github.com/stan-dev/stan into feature/stagnant-model-bugs-vol2
adding a model test for stagnant2. not adding one for stagnant due to slow convergence.
Merge pull request #114 from stan-dev/feature/stagnant-model-bugs-vol2

Feature/stagnant model bugs vol2