made cursor invisible in IE
made cursor invisible in IE

fixes #18
xtermjs/xterm.js,cjordog/NRLWebsite,Tyriar/xterm.js,cjordog/NRLWebsite,xtermjs/xterm.js,akalipetis/xterm.js,akalipetis/xterm.js,xtermjs/xterm.js,akalipetis/xterm.js,sourcelair/xterm.js,xtermjs/xterm.js,cjordog/NRLWebsite,Tyriar/xterm.js,cjordog/NRLWebsite,sourcelair/xterm.js,akalipetis/xterm.js,xtermjs/xterm.js,rwos/xterm.js,Tyriar/xterm.js,rwos/xterm.js,sourcelair/xterm.js,Tyriar/xterm.js,Tyriar/xterm.js,sourcelair/xterm.js