grafx - Extensible Java Graphics Package Code

Tidying up some line-drawing issues in 3D rendering library. Still need to
handle the cases of degenerate lines, where only one pixel gets turned on, and
also need to handle the optimization of line-drawing, where the endpoints pairs
are given special attention w.r.t. z and color bounds, and the inner pixels
are rendered faster.

Adding some comments to RasterFloatGraphics.

Besides modification of some comments, revising pixel() slightly to keep
functionality the same but having the code match code in alias() more closely.

Revising pixel() to match what's in RasterFloatGraphics, and adding the pixel
boundary functions, again copied and pasted from RasterFloatGraphics.

Making a change to function pixel() which [theoretically] keeps it identical
in functionality (in the usable range at least) but makes it more "similar" to
alias() code.

Adding class TwoPixelLineSanityTest.

Reformatting the main comment.

Revising comment related to line drawing boundary conditions.

Removing the commented out println() statements.

Documenting the findings in error case.