2PLOT: plot rectangle - draw a rectangle

Usage: plot rectangle <x1> <y1> <x2> <y2>

draws a rectangle with corners (x1,y1), (x2,y1), (x2,y2) and (x1,y2). 
This command can also be used in list mode, where x1, y1, x2 and y2 
are four vector expressions. In list mode, the command can also be 
used without parameters. In this case a histogram bar, is drawn for 
each point in the list columns.
