Interpolation of overlaid domains

[jderouillat]

In the special case where nodes of source and destination domains are mainly overlaid, domain interpolations can produce very small but not negligible errors.
In the provided case, the destination square_domain is a 36 x 36 domain while the source is a 36 x 18 (with the same origin).
A zoom on FIELD2D_INTERPOLATE[j=1:4,l=1] highlights this small error.

Using a domain with shifted nodes (for instance with a destination of 34 x 38 nodes) display a smoothed results.