[Ipopt] Ipopt maintenance release 3.12.6

[Stefan Vigerske]

Hi,

I just created a new Ipopt maintenance release.
If you were using a recent Ipopt version successfully, then there is no 
need to update.

Here is a list of changes:
- better support for custom algorithm development [r2659]
   (by Gabriel Hackebeil), see https://github.com/coin-or/Ipopt/pull/5

- extend build system to work without Fortran compiler [r2660,r2661]
   If no Fortran compiler is available (F77=unavailable), then the build
   system checks for functions in Blas, Lapack, and Pardiso via C
   linkage. This seems to work when using the Intel MKL, thus allowing
   to build Ipopt with C/C++ compilers and MKL only.
   The linear solver loader and the CuteR interface are disabled when
   no Fortran compiler is available. A user may have to adjust the
   definition of F77_FUNC in Ipopt/src/Common/IpoptConfig.h.

The source tarballs should be available tomorrow.

Enjoy,
Stefan