gpxtest.icn: Program to test graphics procedures

This program exercises a wide variety of graphics operations.  Several
independent output tests are run in square cells within a window.  The
resulting image can be compared with a standard image to determine its
correctness.

The "Dialog" button brings up an interactive dialog box test; the
"Quit" button exits the program.

Some variations among systems are expected in the areas of fonts,
attribute values, and availability of mutable colors.  The first test,
involving window resizing, produces results that do not exactly fit the
grid pattern of the other tests; that is also expected.

This program is designed for a color display, but it also works on
monochrome systems.