grafx - Extensible Java Graphics Package Code

Fixing call of RasterDepthGraphics constructor in ZMinMaxTest, since API
change.

In RasterDepthGraphics, increasing s_zBits from 16 to 24. No longer passing in
z buffer to constructor; it's being instantiated under the hood.

Adding a Javadoc comment explaining nature of zFront and zBack.

Adding new class, ZMinMaxTest.

Removing the m_modRect calculations from RasterDepthGraphics. Such a feature
does not really go well with 3D graphics.

Changing the sensitivity of user interface in Donut.

Well apparently that code needed a slight '++' correction.

First attempt at adding flat shading version of fillPolygon() which is
optimized just for that. This may not even compile; definitely not tested, but
in theory it may just all work.

Unwinding some loops to improve performance of Gouraud fillPolygon(), renaming
some variables for clarity.

Paving the way for improved performance flat shading.