missing graticule lines for Z axes

[ACManke]

Graticule lines are not drawn across the plots at the tic marks on the depth axis.

yes? set data levitus_climatology
yes? fill/y=0/grat temp
yes? fill/y=0/vlimits=0:5000:500/grat temp

The same thing happens with a z-y plot and a 1-D line plot in Z. If we regrid to a regularly spaced Z axis the behavior is unchanged.

See also #129

@ryofurue

[ACManke]

This bug crept in with PyFerret v7.45, where a change was made to draw tic marks on top of any graticule lines, to make sure that tic marks are nice and visible, especially when drawing tic marks inside the plot box. For depth axes, there is a test for whether the z value is between the first and last values (so we don't accidentally draw a graticule slightly outside the plot box). This test was wrong for a depth axis. For these axes, the Z values run, for instance, from 5000 to 0 with a negative delta-value between tics, and that was done incorrectly.

There is currently no way to get the horizontal graticule lines for depth axes, but the fix is now in ppl/plotlib/yaxis1.F A new test is also added to the benchmark suite