fix terminal monitor not working for wrapped lines

package.json

@@ -110,7 +110,7 @@
         "c9.ide.run.debug.xdebug": "#a1b39e0ac4",
         "c9.ide.save": "#1ab1840513",
         "c9.ide.scm": "#ca3c94b84f",
-        "c9.ide.terminal.monitor": "#a0d1f02991",
+        "c9.ide.terminal.monitor": "#021b290e91",
         "c9.ide.test": "#a282ec1619",
         "c9.ide.test.mocha": "#fc053b23d2",
         "c9.ide.theme.flat": "#81dadeee55",

plugins/c9.ide.terminal/aceterm/libterm.js

@@ -301,8 +301,10 @@ Terminal.prototype.scroll = function() {//TODO optimize lines
   var row;
 
   if (++this.ybase === Terminal.scrollback) {
-    this.ybase = this.ybase / 2 | 0;
-    this.lines = this.lines.slice(-(this.ybase + this.rows) + 1);
+    var lineCount = this.ybase / 2 | 0;
+    this.emit("discardOldScrollback", lineCount);
+    this.ybase -= lineCount;
+    this.lines = this.lines.slice(lineCount);
   }
 
   this.ydisp = this.ybase;