ChangeLog

======================= Log Before Release =====================================
2020-02-15:
  * Use new mpicc branch of rabit.
  * Test examples with MS-MPI.
  * Run R CMD check --as-cran
  * Remove unnecessary export functions.

2019-11-08:
  * Wrap original examples in SPMD via 'pbdMPI::mpiexec()'.
  * Rename the package to 'pbdXGB'.

2019-10-27:
  * First try to build with MS-MPI which has MPI C library only.
  * Test with Drew's 'kasaam' example via 'get.jid()'.
  * Put MPI C++ library back as an option via puting '--enable-mpi-cxx'
    in 'R CMD INSTALL --configure-args=...'.

2019-10-15:
  * First try to combine with MPI C library.
  * Alter rabit MPI engine to get rid of MPI C++ library.
  * Check with cop implementations for MPI_Datatype and MPI_Op.
  * Fix typos.

2019-09-xx:
  * First try to combine xgboost with MPI using pbdMPI.
  * Load 'libmpi_cxx.so' for OpenMPI from 'zzz.r'.

2019-08-xx:
  * Create 'xgboost.mpi' with core 'xgboost' functions only.
  * Alter all '.Call(...)' to explicitly call the C/R API.
  * Enable mpicxx in OpenMPI and MPICH3 and test with them.