[Users] New thorn NoMPI

[Erik Schnetter]

I have just committed a new thorn CactusUtils/NoMPI. This thorn
contains a fake MPI implementation for much (but not everything) of
MPI's functionality. It provides only a trivial implementation that
runs on a single processor. NoMPI can be used to use an MPI code on
systems where there is no MPI conveniently available, e.g. on laptops
or workstations.

To use this thorn, add #include <nompi.h> to your source code, and
"uses include header: nompi.h" to the interface.ccl. Thorn NoMPI will
automatically switch itself off if a real MPI implementation is found,
so that it can be safely used all the time.

My main goal was to make Carpet run on such systems, without having to
add #ifdefs around each MPI call. Thorn NoMPI is not quite trivial,
since certain functionality (e.g. MPI datatypes) still need to be
supported.

-erik

-- 
Erik Schnetter <schnetter at cct.lsu.edu>   http://www.cct.lsu.edu/~eschnett/