Factor Tnlp class for both solver into one meta-class.
Fix iRow/jCol filling in Tnlp::eval_jac_g.

Original patch by jorisv.
Use a vector instead of a matrix to store constraint value.

Original patch by jorisv.
Add a test for ipopt plugin.
Allows the user to define his own intermediate_callback implementation.

Original patch by jorisv.
Fix signed/unsigned comparison warning.
Update test values.