Add in architecture checking IOobjects read.

Placeholder for topics related to "arch" handling (endian, label and scalar sizes) that was added for v1612. We now emit arch hints such "LSB,label=32,scalar=64", but don't do anything with them on input.

The first point is to simply to check their types on input: "arch" exists and is identical to the current OpenFOAM configuration. The next would be a special-purpose foam-convert utility. Handling a change from int64 to int32 might only work in very special cases. For example, when snappy needs 64-bit labels because the input surfaces have so many points and faces, but the resulting mesh would still fit with int32.