Merge branch 'develop' of https://github.com/stan-dev/stan into develop

Merging upstream develop.
Merge branch 'develop' of https://github.com/stan-dev/stan into develop
Merge branch 'develop' of https://github.com/stan-dev/stan into develop
Changed name of template parameter to avoid compiler bug on Mac OS X 10.7.5.
Merge pull request #569 from stan-dev/bugfix/issue-568-epil

Fixes #568.