Pstream: added maxCommsSize setting to do (unstructured) parallel transfers in blocks.
Tested:
- with maxCommsSize 0 produces exactly same result as plus.develop
- compiles with label64
- with maxCommsSize e.g. 3 produces exactly same result as plus.develop
- with maxCommsSize=0 exactly the same messages (with Pstream::debug = 1) as plus.develop
See merge request !85
This is controlled by the setting maxCommsSize in etc/controlDict which
specifies the max number of bytes per exchange. If set to <= 0 it
is ignored. This max size of messages is important when doing e.g.
load balancing which can send over whole meshes.
