line-plot overlays and tic mark oddities for high-res time

[AnsleyManke]

A PLOT command listing several variables together gets the time axis scaling right, but for time axes on scales of ~minutes, plots done with " PLOT first_var; PLOT/OVER second_var" does not. Ascaling is wrong and the line sample for auto-generated line key are missing.

In addition for some time ranges on the plot, the minor tic marks are not drawn at even sub-intervals of the labeled tics.

define axis/t=30-aug-2017:1-sep-2017:1/units=minutes taxis
let var1 = cos(L[gt=taxis]/30)
let var2 = sin(L[gt=taxis]/10)

set view upper
plot/t="30-aug-2017:01:00":"30-aug-2017:03:00" var1, var2
set view lower
plot/t="30-aug-2017:01:00":"30-aug-2017:03:00" var1
plot/over var2

[AnsleyManke]

This is fixed in pltit.F, taxis4.F, tayis4.F