grafx - Extensible Java Graphics Package Code

Revising comment related to line drawing boundary conditions.

Removing the commented out println() statements.

Documenting the findings in error case.

Holy crapola I finally found an error case. It's some sort of error, I don't
know which.

Getting close to coming up with the error case.

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.