grafx - Extensible Java Graphics Package Code

Committing some commented-out println() statements in drawLinePosDxDy() which
explains the step-by-step process of pixel selection.

I am really struggling with this test code. Committing what I've got.

Adding a long comment regarding the possibility that an end pixel won't get
turned on.

Caching m_dx and m_dy in line drawing, 2D graphics.

Improving the degenerate line handling in 2D rendering.

Strarting to improve 2D line rendering code by removing extra checks that are
no longer necessary.

Adding comment block announcing experimental work in progress.

Adding new test code which exposes a bug: OnePixelSteepLine.

Backing out the last two commits in RasterDepthGraphics. I was modifying the
wrong section of code, and I just realized that first we should correct an
anomaly where a very short line segment which spans a very large z distance,
which has both endpoints aliased to the same pixel, should be handled more
correctly; the pixel in front should be given priority.

Unrolling the first iteration of 'while' loop in line drawing improvement
experimental code block.