Fixed a Math.multiply Math.devide overflow bug[1]

[1] http://nand2tetris-questions-and-answers-forum.32033.n3.nabble.com/Tools-Updated-OS-Math-vm-file-td4028218.html
Fixed the horizontal-scroll problem

Patch[1] provided by Kyle Smith.

[1] http://nand2tetris-questions-and-answers-forum.32033.n3.nabble.com/Fix-Horizontal-Scroll-in-Subwindows-tp124410.html