add limitSigDigs() function to number's prototype. tests included

git-svn-id: http://svn.openlayers.org/trunk/openlayers@1008 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Util.js

@@ -707,6 +707,22 @@ Array.prototype.indexOf = function(element) {
     return index;    
 }
 
+/**
+ * @param {int} sig
+ * 
+ * @returns The number, rounded to the specified number of significant digits.
+ *          If null, 0, or negaive value passed in, returns 0
+ * @type int
+ */
+Number.prototype.limitSigDigs = function(sig) {
+    var number = (sig > 0) ? this.toString() : 0;
+    if (sig < number.length) {
+        var exp = number.length - sig;
+        number = Math.round( this / Math.pow(10, exp)) * Math.pow(10, exp);
+    }
+    return parseInt(number);
+}
+
 /**
  * @param {String} id
  * @param {OpenLayers.Pixel} px