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Copyright (c) 2011 OpenCFD Ltd.

Some background on the new structure to synchronise point and edge data. The
building blocks:
- globalIndex : globally consecutive numbering of (untransformed) data. It
consists of a single label which starts at 0 on processor 0 and is numbered
consecutively on consecutive processors. The globalIndex class contains
functions to convert to/from processor and local index.

- globalIndexAndTransform : all the transformations in a mesh. Because the
transformations (cyclics, processorCyclics) need to fill space there can
be only three independent transforms. This class contains functions to encode
local index,processor and transformation into a labelPair.

- mapDistribute : contains constructors from local and remote data and
works out a compact storage scheme and returns corresponding indices into
the local storage and calculates a scheduling to get the local and remote
data into the local storage. The wanted data is
    - untransformed: labelList(List) in globalIndex numbering
    - transformed: labelPairList(List) in globalIndexAndTransform
See also mapDistribute.H

- globalMeshData : works out and stores a mapDistribute to get hold
of coupled point or edge data:
    - globalPointSlavesMap() : the map to get all coupled point data
    into a compact form
    - globalPointSlaves : per point (on the patch of coupled faces) the
    indices into the compact data corresponding to untransformed connected
    points
    - globalPointTransformedSlaves : same but for transformed connected
    points
See e.g. syncPointData which applies a reduction operator to data on
coupled points. Note that it needs to know whether the data is a position
(since might need separation() vector).

These structures get used in e.g.
- syncTools : general synchronisation on points,edges, faces. The point and
edge synchronisation are thin wrappers around the globalMeshData functionality.
- volPointInterpolation : uses a mix of globalMeshData (for synchronising
collocated points) and patch-wise (for separated points).