constrain DSG trajectory, profile plots minor bugs

[AnsleyManke]

For profile and timeseries DSG data the native plots constraining along the native direction works fine,

yes? use pmelTao5daySst_timeseries_dsg
yes? plot/T=15-jan-2017:15-feb-2017/m=1:3 t_25

yes? use WestCoastCarbon_profile_dsg.nc
yes? plot/z=10:400/m=1:3 pco2

and also for profile and timeseries constraining in X and Y works fine: choosing features by station location

yes?  use pmelTao5daySst_timeseries_dsg
yes? plot/x=155:165/y=-10:0 t_25

But for Trajectory plots, X-Y-T constraints select the right data, but the plot axis in Y doesn't adjust to the constrained subset.

yes? use socat_trajectory_dsg

! this is correct
yes? plot/t=02-APR-2017:01-jun-2017 temp ; go fland

! These select the right data but the map region shows the whole original range in Y
yes? plot/x=170W:155W temp; go fland
yes? plot /y=55:70 temp; go fland

[AnsleyManke]

This is fixed in plt/dsg_traj_plot_set_up.F and new tests added to the benchmarks.