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When profiling the GPU version, NVTX can be used to highlight the
corresponding regions of the code in the timeline of the profiling tool
(nvvp or nsight systems). This is very useful to correlate what happens
on the GPU with what part of the code we are in.

ELPA can now be linked against a 64bit integer version of MPI and
ScalaPack. This is an experimental feature

The following points are still to be done
- does not work with real QR-decomposition
- generalized routines return wrong results
- the C tests and the C Cannon algorithm implementation do not
  work (no 64bit header files for MPI *at least* with Intel MPI)

also introducing --with-likwid parameter to the configure script

Can be used to compile with likwid and to enable the likwid to measure
performance of individual compute steps

This solves issue #66

The GPU initialization is actually quite constly, e.g. on Minsky it
takes roughly 0.7s. That is hurting performance for small matrices.
Thus a check has been added and now GPU should be initialized only the
first time.

Anything if it makes Andreas happy :)

whether or not a step is actually computed is decided with logicals
(default all 3 steps are computed). This makes the implementation
of "solve_tridi" and "eigenvalues_only" a bit cleaner in the future