Matrix3D bug fix

["Leonard McMillan" <mcmillan@lcs.mit.edu>]

There was a bug in the Matrix3D.java code in the copy() method. You will not
run into it if you use the supplied Applet code. If, however, you have added
any push() or pop() calls to the Applet, you might have noticed an
ArrayStoreException.

I have corrected the bug and updated the code on the Project #4 page. I have
also added the MatrixStack.java to do a full stack dump. You might want to
download both of these updates or from the following links.

http://graphics.lcs.mit.edu/classes/6.837/F00/Project4/Matrix3D.java
http://graphics.lcs.mit.edu/classes/6.837/F00/Project4/MatrixStack.java


I am sorry for the confusion,
Leonard