deleting declared but unused variables, removing dummy arguments,
changing variables to double precision.
Not touching: uninitialized and more complicated warnings.

Attempted to generalize define_isostasy_bc.f90 to be able to be called by any defined velocity B/C option

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