and msh

create new testcase: check if tracer offline is ok (solve hydro and tracer, then tracer offline and compare tracer and tracer offline)
It also uses importIdx (on a tracer)
modification in slim.py:
	* hydro_sol in tracer has the same initial conition as the hydro (it was 0)
	* the file for offline are imported by means of importMsh instead of importIdx

+ add export rho

                     (2) Code does not crash without PNETCDF

+ update Danilov test case

+ small fixes

(constant flow at open bnd not done in prepro. Bathymetry from 3d mesh
still unavailable)
This is a non checked commit.
3D interface is not veriried yet