Plot y over x fails when applying ROI on dataObject

[Robin Hahn]

The ROI of an object is not considered when plotting y values over x values, or the displayed values do not correspond to the expectation. Probably it is not checked whether the data set of the x values is continuous. The following code should display a line:

a=dataObject([5,2])
a[0,0]=5
a[1,0]=6
a[2,0]=7
a[3,0]=8
a[4,0]=9
b=dataObject([5,2])
b[0,0]=1
b[1,0]=2
b[2,0]=3
b[3,0]=4
b[4,0]=5

plot1(b[:,0],a[:,0])

[Robin Hahn]

fixes #20 : y-direction of x-vector was never considered in xy-plot

→ <<cset c039375cbde1>>

[M. Gronle]

fixes #20 : y-direction of x-vector was never considered in xy-plot

→ <<cset 7407e678234c>>