Merging into develop

Merge branch 'develop' of https://github.com/stan-dev/stan into develop
Merging branch
Merge branch 'develop' of https://github.com/stan-dev/stan into develop
Efficient implementation of multiply_lower_tri_self_transpose.hpp
Modified test file to include symmetry checks on large matrices
Merge branch 'develop' into bugfix/issue-1121-multivariate-error
updated test
Merging
Merge branch 'bugfix/issue-1121-multivariate-error' of https://github.com/stan-dev/stan into bugfix/issue-1121-multivariate-error
Removed old method from unit/math/matrix test, changed the large L matrix generator function, added the test to agrad/rev/matrix test, cleaned up commented code
Merge branch 'develop' of github.com:stan-dev/stan into develop
small fix for beta distribution error messages
Added neg_binomial_2_cdf + tests
Added neg_binomial_2_cdf_log + tests
Added neg_binomial_2_ccdf_log + tests
added neg_binomial_2 cdfs to functions signature and syntax tests
added neg_binomial_2 cdfs to manual
Fix misc typos in manual and RELEASE notes

- cbind and rbind to append_col and append_row
- reference to ode_solve changed to integrate_ode
- fix font rendering problems in boolean operators
added emacs temporary files to gitignore
Merge pull request #1143 from stan-dev/bugfix/issue-1139-typos-manual-etc

Bugfix/issue 1139 typos manual etc
Merge pull request #1144 from stan-dev/feature/additional-patterns-to-gitignore

added emacs temporary files to gitignore
Improvements and fixes to neg_binomial_2 cdfs