clean up preprocessor directives

Currently we have the following preprocessor directives in the code (.e.g. #ifdef ...):

• GFORTRAN
• GFORTRAN41
• INTEL
• PGI
• ABSOFT
• MPI

They are activated correctly apart from GFORTRAN41, which we probably should drop anyway. 'PGI' is not tested, but claimed to be in jams-fortran. 'ABSOFT' is not tested in jams-fortran also.