- used low-level MPI gather, but the wrapping routine contains an
additional safety check for is_contiguous which is not defined for
various std::pair<..> combination.
So std::pair<label,vector> (which is actually contiguous, but not
declared as is_contiguous) would falsely trip the check.
Avoid by simply gathering unbundled values instead.
- change contiguous from a series of global functions to separate
templated traits classes:
- is_contiguous
- is_contiguous_label
- is_contiguous_scalar
The static constexpr 'value' and a constexpr conversion operator
allow use in template expressions. The change also makes it much
easier to define general traits and to inherit from them.
The is_contiguous_label and is_contiguous_scalar are special traits
for handling data of homogeneous components of the respective types.
