#177 Fix incomplete cursor capability for the wxwidgets, qtwidget, and xcairo devices

[Alan W. Irwin]

Example 20.03 does not allow the user to set the cursor for the wxwidgets, qtwidget, and xcairo devices. Note alll three devices have sufficient interactive capability to print out cursor position results for example 1 with the -locate option, but all three devices fail to allow the user to select a region in example 20.03. So all three (and wingcc and wincairo if they show similar problems with this page) should be updated to have the same cursor capabilities as -dev xwin which allows the user to select with the cursor a subset of the plot to display for this page.