Bugfix/issue 904 eigen assert bugs

#### Summary:

Updates Stan so it compiles with EIGEN_NO_DEBUG not defined. The fixes are mostly in tests.

#### Intended Effect:

Allows all tests to pass when EIGEN_NO_DEBUG isn't defined.

#### How to Verify:

Run unit tests.

#### Side Effects:

Stan's makefile now does not have EIGEN_NO_DEBUG as part of its flags. I just verified that CmdStan has it defined.

#### Documentation:

Not user facing.

#### Reviewer Suggestions:

Anyone.