values at longitude boundaries, in case of periodicity.

Add argument "periodic" to procedures get_snapshot and
set_all_outerm. Duplicate values at longitude boundaries in ssh, u, v
if periodic. set_all_outerm can now call local_extrema with periodic
true. In procedure set_all_outerm, we shift the longitudes of outside
points if necessary.

In program test_get_snapshot, define periodic from step and nlon.

and signalling NaN so we cannot use the -ffpe-trap=invalid option.

Accept that we might not be able to compute the mean speed on the
outermost contour: there might be undefined values of velocity
around. In that case just use the contour coming from
max_speed_contour_ssh.

Add quiver_key in plot_snapshot.py.

New test for region 5.

For ssh, missing value is huge(0.). We have to take a large value
because Contour_531 has an argument zmax for missing values. For
velocity, missing value is a quiet NaN. We have to take this because
we need to know if the interpolation procedure in mean_speed has not
used any missing value and we do not want to alter the interpolation
procedure itself.

In local_extrema, we accept as local extrema only points with 8 valid
values around them.

When we look for the maximum speed contour, we are hoping that good
contours do not englobe missing values. If this happens, the program
aborts.

When computing the mean speed on a contour, we are hoping that the
interpolation of speed on contour points does not use missing
values. If this happens, the program aborts.

Draw coastlines in plot_snaphot.py. At the same time, this allows the
use of any projection.

procedure get_eddy), with corresponding test.

Take into account the fact that derived type polygon became polyline
in library Contour_531.

Use new procedure null_polyline from library Contour_531.

Correct a sneaky bug in mean_speed: the last point in the polygon
array is a duplicate of the first point, do not take the last point
into account when averaging (and interpolating). Discovered this bug
because the mean speed was not exactly the same for equivalent
polygons with circular permutation.

Change philosophy for the tests: read whole NetCDF variables, prepare
different NetCDF files for different geographical regions if needed;
read all data from file or namelist; read names of files on command
line.

Use generic test_program.sh (which is out of this project) instead of
the specific tests_detection_eddies.sh.