Rename _getKey to $$getKey

Author: katowulf

src/FirebaseArray.js

@@ -5,7 +5,7 @@
    * manually invoked. Instead, one should create a $firebase object and call $asArray
    * on it:  <code>$firebase( firebaseRef ).$asArray()</code>;
    *
-   * Internally, the $firebase object depends on this class to provide 5 methods, which it invokes
+   * Internally, the $firebase object depends on this class to provide 5 $$ methods, which it invokes
    * to notify the array whenever a change has been made at the server:
    *    $$added - called whenever a child_added event occurs
    *    $$updated - called whenever a child_changed event occurs
@@ -15,8 +15,9 @@
    *    $$process - called immediately after $$added/$$updated/$$moved/$$removed
    *                to splice/manipulate the array and invokes $$notify
    *
-   * Additionally, there is one more method of interest to devs extending this class:
+   * Additionally, these methods may be of interest to devs extending this class:
    *    $$notify - triggers notifications to any $watch listeners, called by $$process
+   *    $$getKey - determines how to look up a record's key (returns $id by default)
    *
    * Instead of directly modifying this class, one should generally use the $extendFactory
    * method to add or change how methods behave. $extendFactory modifies the prototype of
@@ -162,7 +163,7 @@
          */
         $keyAt: function(indexOrItem) {
           var item = this._resolveItem(indexOrItem);
-          return this._getKey(item);
+          return this.$$getKey(item);
         },
 
         /**
@@ -176,7 +177,7 @@
         $indexFor: function(key) {
           var self = this;
           // todo optimize and/or cache these? they wouldn't need to be perfect
-          return this.$list.findIndex(function(rec) { return self._getKey(rec) === key; });
+          return this.$list.findIndex(function(rec) { return self.$$getKey(rec) === key; });
         },
 
         /**
@@ -349,7 +350,7 @@
          * @returns {string||null}
          * @private
          */
-        _getKey: function(rec) {
+        $$getKey: function(rec) {
           return angular.isObject(rec)? rec.$id : null;
         },
 
@@ -364,7 +365,7 @@
          * @private
          */
         $$process: function(event, rec, prevChild) {
-          var key = this._getKey(rec);
+          var key = this.$$getKey(rec);
           var changed = false;
           var pos;
           switch(event) {