Changing write_global_output so that the current output file is always kept
temporarily and deleted after the next output file was written. When
time = n*savstep+savoffset the files are kept permanently.

added variable calc_comp_velo, which is used to determined when compaction velocity should (or should not) be calculated

Added options for restarting with compaction output. Modified code to not read/write output for certain fields when they are not used (isostasy, compaction, nest)

Added option of using previous steps strain rate to soften materials, updated only at the end of the previous step

Added output of yield_ratio and did minor cleanup; moved ziso stuff into bc_definition derived data type

Added Jean's subroutine for moving surface points along a normal to coincide with the zero of the LSFs

Tweaked output so that all output variables are always written, with zero values when the calculation is not performed

Reverted to using 'include mpif.h' as the use of mpi.mod requires the MPI module be compiled with the same compiler as the DOUAR source, which is not true on geodyncomp