Fix feedback loop between code.style.width and lineSpace.offsetWidth

This would be visible in the activeline demo, where the colored line would get
shorter and shorter for each display update.

lib/codemirror.js

@@ -767,7 +767,7 @@ var CodeMirror = (function() {
       var textWidth = stringWidth(maxLine);
       lineSpace.style.width = textWidth > scroller.clientWidth ? textWidth + "px" : "";
       // Needed to prevent odd wrapping/hiding of widgets placed in here.
-      code.style.width = (lineSpace.offsetWidth + lineSpace.offsetLeft) + "px";
+      code.style.width = scroller.scrollWidth + "px";
 
       // Since this is all rather error prone, it is honoured with the
       // only assertion in the whole file.