specified to be cached to avoid unnecessary recalculation.

equivalent to the 'none' entry in fvSchemes and relaxation factors must be
provided for all fields which might require one.  If it is set to a value
between 0 and 1 this value is used as the default relaxation factor.

See http://openfoam.cfd-online.com/cgi-bin/forum/show.cgi?126/11559

- regIOobject: don't re-register an unregister object on rename/assignment
- Hasher: split-off HasherInt with uint32_t specializations
- IOobject: writeBanner/writeDivider return Stream for easier chaining.

... also dropped some namespace bracketing while I was at it.