outputs optimization to file. fixed by flushing and closing output stream appropriately.
Add return code strings for BFGS optimizer.
BFGS parameter changes.  Add tol_obj, tol_param and tol_grad parameters.  Change stepsize to init_alpha as it better reflects its use.
pulling out common code
updated return codes for bfgs optimization
Clean up BFGS code and messages a bit further.
Merge branch 'develop' into feature/issue-259
Fix bug introduced in recent cleanup.
Merge pull request #261 from stan-dev/feature/issue-259

Fixes #259. Optimization broken in develop (pull request)