ENH: additional handling for out-of-range sampling (#1891)

- when sampling onto a meshed surface, the sampling surface may be
  outside of the mesh region, or simply too far away to be considered
  reasonable.

  Can now specify a max search distance and default values for samples
  that are too distant.
  If a default value is not specified, uses Type(Zero).

  Eg,

      maxDistance     0.005;
      defaultValue
      {
          "p.*"   1e5;
          T       273.15;
          U       (-100 -100 -100);
      }