Use MPI Get_elements_x() for message sizes

• more/better error messages when trying to receive messages that exceed INT_MAX

• internal accounting for message sizes now corresponds to label, which is the same as List<T>::max_size() represents to avoid truncation as int

• style changes (eg, "buffered" instead of mis-leading "blocking") for communication type.

changed milestone to %v2406

requested review from @kuti

assigned to @Mattijs

• includes compatibility enum blocking as alias for buffered (ie, old code will still compile).

The main, interesting changes are in src/Pstream/mpi.

requested review from @andy and removed review request for @kuti

@Prashant - I don't expect any real issues with this since MPI_Get_elements_x() is even in openmpi-1.10.4 as well as msmpi-10.0, but if you happen to know of a particularly ancient MPI on one of your systems where it may fail to compile or run, it would be good to know.

added 3 commits

• 7f355ba3 - STYLE: communication name "buffered" instead of "blocking"
• 7b38b148 - STYLE: use PstreamBuffers default construct
• b2bbc154 - ENH: use MPI Get_elements_x() for message sizes (#3152)

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mentioned in commit 7dc9ccdc

merged

resolved all threads