Restrictions on struct derived type.

Some options allowed for derived data types in the C and Fortran binding are deleted in mpiJava. The Java VM does not incorporate a concept of a global linear address space. Passing physical addresses to data type definitions is not allowed. The use of the MPI_TYPE_STRUCT datatype constructor is also restricted in a way that makes it impossible to send mixed basic datatypes in a single message. Since, however, the set of basic datatypes recognised by MPI is extended to include serializable Java objects, this should not be a serious restriction in practice.