* Also rename corresponding C sources.

* This is only one step mandated by the brain-dead behaviour of the
  NAG and PGI compilers respectively.

- Removed unnecessary, misleading comments
- initialized boundary of s

- removed some unnecessary variables

* Lines must be at most 132 characters long, less than 80 is preferred.
* Such problems might in some cases only occur when __FILE__ expands
  to a long string.

- IBM xlf doesn't allow for this kind of functions
- The matrix stencil now has a shift property to simulate the old behavior
- Additional shifted versions of all matrix stencil were necessary

- added an apply_stencil function that does what it says
- renamed get_lambda_min_max to calc_lambda_min_max
- new get_lambda_min_max returns the values from the config

- added new file solver_public.f90

CG with different preconditioners tested

Red/Black SSOR has known best relaxation value of 1, therefore it makes no sense.

This was necessary after rebase

Internal datastructures are now in solver_internal.f90 which shouldn't be imported
by external applications.

Vectorize in back substitution the calculation of the last few entries of a column

In backward substitution the first few entries in a column were incorrectly calculated for fill-in p >= 2

The last s_l entries of a colum are now updated column-wise instead of row-wise

Special treatment of last column in backward substitution to save some operations

When assembling the ICC matrices ICC_W and ICC_S there were entries written in ISS_S(k,i,je) (je!!!)
which shouldn't been there. Adding two IF (...) EXIT statements in the loops generating the entries
in the secondary and outer diagonal solved this.