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- fix bug in storing/loading grids with shape attribute set.
- change equality check of grids to be more flexible. Now only a match of the
tuples gpi, lon, lat, cell is checked. The order does no longer matter.
- Shape definition changed to correspond to what one would expect. Now a 1x1
regular global grid has the shape (180, 360) corresponding to the 180 rows and
360 columns that the array has. This was necessary since the genreg_grid
function produced grids with wrong lon2d, lat2d arrays because the shape was
not correct