cannot include the PMPI_WTIME|WTICK functions in the external and
double precision statements because some compilers complain about
this. Instead, we need to use the macro that is defined by
configure.ac (MPIF_H_PMPI_W_FUNCS). This unfortunately means that we
need to generate mpif.h (in addition to mpif-config.h) because the
"external" statement is toxic to F90 compilers.
This commit was SVN r10464.