Cleaning up code in interactiveLayer -> mousemove, regarding

the IE 10 hack. It turns out that d3.event.offsetX/Y contains
the relative mouse coordinates needed. Using those instead.

src/interactiveLayer.js

@@ -19,7 +19,7 @@ nv.interactiveGuideline = function() {
 
 	//Private variables
 	var previousXCoordinate = null
-	isMSIE = navigator.userAgent.indexOf("MSIE") !== -1
+	isMSIE = navigator.userAgent.indexOf("MSIE") !== -1  //Check user-agent for Microsoft Internet Explorer.
 	;
 
 
@@ -55,18 +55,16 @@ nv.interactiveGuideline = function() {
 				          var mouseX = d3mouse[0];
 				          var mouseY = d3mouse[1];
 				          
-				          if (isMSIE && (mouseX < 0) || (mouseY < 0)) {
+				          if (isMSIE) {
 				          	 /*
-								D3.js (or maybe SVG.getScreenCTM) has a nasty bug in Internet Explorer.
+								D3.js (or maybe SVG.getScreenCTM) has a nasty bug in Internet Explorer 10.
 								d3.mouse() returns incorrect X,Y mouse coordinates when mouse moving
-								over a rect in IE.  THe coordinates are off by 25% of the element's offsetLeft position.
-								For instance, if the <rect> is 100px left of the screen, the left most mouse point returned
-								will be -25 on IE. This hack solves the problem.
+								over a rect in IE 10.
+								However, d3.event.offsetX/Y also returns the mouse coordinates
+								relative to the triggering <rect>. So we use offsetX/Y on IE.  
 				          	 */
-				          	 var offsetLeft = offsetParent.getBoundingClientRect().left;
-						     var offsetTop = offsetParent.getBoundingClientRect().top;
-				          	 mouseX = mouseX + 0.25 * offsetLeft;
-				          	 mouseY = mouseY + 0.25 * offsetTop;
+				          	 mouseX = d3.event.offsetX;
+				          	 mouseY = d3.event.offsetY;
 				          }
 				          
 				          var pointXValue = xScale.invert(mouseX);
@@ -84,7 +82,7 @@ nv.interactiveGuideline = function() {
 				          
 				          if (isMSIE) {
 				          	/* 
-				          	  On IE9+, the pointer-events property does not work for DIV's (it does on Chrome, FireFox).
+				          	  On IE 9+, the pointer-events property does not work for DIV's (it does on Chrome, FireFox).
 				          	  So the result is, when you mouse over this interactive layer, and then mouse over a tooltip,
 				          	  the mouseout event is called, causing the tooltip to disappear. This causes very buggy behavior.
 				          	  To bypass this, only on IE, we check d3.event.relatedTarget. If this is equal to anything in the tooltip,