create a duplicate type, because any duplicate type lose the PREDEFINED flag.
An MPI_LB (respectively MPI_UB) without the PREDEFINED tag is useless, as it's
not the a marker anymore. The solution is to return the same pointer, but once
the reference count has been increased. In order for this to work, I allowed
the destruction to check for the reference count of an object before complaining
about destroying a predefined type.
This fixed ticket #317.
This commit was SVN r13942.