Implemented the N^2 condensed Hessian factorization, nx^3 free...

... for the CN2_FACT... solver.
Fixed a bug related to export of RT integrators.

@rienq please take a look
Merged stable, 855a125
Added "hasCholesky" flag to the qpOASES embedded
Working towards support for external Hessian Cholesky decomposition.
Added API for tunneling the ext. Cholesky decomposition to qpOASES
Added options for decomposition of condensed Hessian.
interfaced Cholesky of the condensed Hessian ...

... to qpOASES based OCP solvers
Fixed printing of ExportVariables of type INT
Optimized export of Cholesky and corr. solver routines...

... used for N^2 factorization.
Updated the CN2_FACT... solver ...

- Optimized export of the condensing and factorization routines for
  long horizons.
Fixing a bug in return value from Cholesky decomposition.
Cleaning the CN2_FACT... solver.
Tuning the N2_FACT... solver
Merge branch 'master' of github.com:mvukov/acado
fixed warning in function.cpp
fixed warning in three-sweeps integrator