Ensure scroll bar is refreshed after erase all in display
Ensure scroll bar is refreshed after erase all in display

Fixes #760

akalipetis/xterm.js,sourcelair/xterm.js,akalipetis/xterm.js,Tyriar/xterm.js,Tyriar/xterm.js,Tyriar/xterm.js,Tyriar/xterm.js,xtermjs/xterm.js,sourcelair/xterm.js,Tyriar/xterm.js,akalipetis/xterm.js,xtermjs/xterm.js,xtermjs/xterm.js,xtermjs/xterm.js,sourcelair/xterm.js,akalipetis/xterm.js,xtermjs/xterm.js,sourcelair/xterm.js