In procedure get_snapshot, encountered rounding error that led to

out-of-range index so add min when calculating urc.

Bug fix in procedure good_contour. polygon_contains_point should not
be called if polyline is not closed.

Procedure polygon_contains_point became unpure so remove pure for
procedure inside_4 too.

In program test_good_contour, read corner and step from namelist
rather than from coordinates in NetCDF file. Makes it possible to use
the same NetCDF file with different coordinates. Also read
outside_points from a file rather than standard input so there is no
need to specify in advance the number of outside points.

Take into account the possibility that no outermost contour was found
in program test_set_outermost_contour. Also, use fixed names for input
files because it is not convenient to require a particular order of
these two files on the command line.