refactor(ngPluralize): minor refactoring to avoid repetition

Move regular expression outside of the `link` function (so it doesn't get
created for every instance of `ngPluralize`.
Replace `RegExp.test + String.replace + String.replace` with `RegExp.exec
+ string concatenation`.

Author: gkalpak

src/ng/directive/ngPluralize.js

@@ -173,24 +173,27 @@
     </example>
  */
 var ngPluralizeDirective = ['$locale', '$interpolate', '$parse', function($locale, $interpolate, $parse) {
-  var BRACE = /{}/g;
+  var BRACE = /{}/g,
+      IS_WHEN = /^when(Minus)?(.+)$/;
+
   return {
     restrict: 'EA',
     link: function(scope, element, attr) {
       var numberExp = attr.count,
           oneTimeCount = (numberExp.charAt(0) === ':') && (numberExp.charAt(1) === ':'),
           whenExp = attr.$attr.when && element.attr(attr.$attr.when), // we have {{}} in attrs
           offset = attr.offset || 0,
-          whens = scope.$eval(whenExp) || {},
-          whensExpFns = {},
+          whens = scope.$eval(whenExp) || createMap(),
+          whensExpFns = createMap(),
           startSymbol = $interpolate.startSymbol(),
           endSymbol = $interpolate.endSymbol(),
-          isWhen = /^when(Minus)?(.+)$/;
+          tmpMatch;
 
       forEach(attr, function(expression, attributeName) {
-        if (isWhen.test(attributeName)) {
-          whens[lowercase(attributeName.replace('when', '').replace('Minus', '-'))] =
-            element.attr(attr.$attr[attributeName]);
+        tmpMatch = IS_WHEN.exec(attributeName);
+        if (tmpMatch) {
+          var whenKey = lowercase((tmpMatch[1] ? '-' : '') + tmpMatch[2]);
+          whens[whenKey] = element.attr(attr.$attr[attributeName]);
         }
       });
       forEach(whens, function(expression, key) {