Make each helper data uniform

Provide @key and @last value for all forms of iteration.

Fixes #910

lib/handlebars/base.js

@@ -117,36 +117,43 @@ function registerDefaultHelpers(instance) {
       data = createFrame(options.data);
     }
 
+    function execIteration(key, i, last) {
+      if (data) {
+        data.key = key;
+        data.index = i;
+        data.first = i === 0;
+        data.last  = !!last;
+
+        if (contextPath) {
+          data.contextPath = contextPath + key;
+        }
+      }
+      ret = ret + fn(context[key], { data: data });
+    }
+
     if(context && typeof context === 'object') {
       if (isArray(context)) {
         for(var j = context.length; i<j; i++) {
-          if (data) {
-            data.index = i;
-            data.first = (i === 0);
-            data.last  = (i === (context.length-1));
-
-            if (contextPath) {
-              data.contextPath = contextPath + i;
-            }
-          }
-          ret = ret + fn(context[i], { data: data });
+          execIteration(i, i, i === context.length-1);
         }
       } else {
+        var priorKey;
+
         for(var key in context) {
           if(context.hasOwnProperty(key)) {
-            if(data) {
-              data.key = key;
-              data.index = i;
-              data.first = (i === 0);
-
-              if (contextPath) {
-                data.contextPath = contextPath + key;
-              }
+            // We're running the iterations one step out of sync so we can detect
+            // the last iteration without have to scan the object twice and create
+            // an itermediate keys array. 
+            if (priorKey) {
+              execIteration(priorKey, i-1);
             }
-            ret = ret + fn(context[key], {data: data});
+            priorKey = key;
             i++;
           }
         }
+        if (priorKey) {
+          execIteration(priorKey, i-1, true);
+        }
       }
     }