Ensure lazy takeWhile works with reverse and last`. [closes #990]

lodash.src.js

@@ -11437,7 +11437,7 @@
             filtered = result.__filtered__,
             iteratees = result.__iteratees__ || (result.__iteratees__ = []);
 
-        result.__filtered__ = filtered || isFilter || (isWhile && result.__dir__ < 0);
+        result.__filtered__ = filtered || isFilter || isWhile;
         iteratees.push({ 'iteratee': getCallback(iteratee, thisArg, 3), 'type': index });
         return result;
       };
@@ -11504,9 +11504,14 @@
     };
 
     LazyWrapper.prototype.dropWhile = function(predicate, thisArg) {
-      var done;
+      var done,
+          lastIndex,
+          isRight = this.__dir__ < 0;
+
       predicate = getCallback(predicate, thisArg, 3);
       return this.filter(function(value, index, array) {
+        done = done && (isRight ? index < lastIndex : index > lastIndex);
+        lastIndex = index;
         return done || (done = !predicate(value, index, array));
       });
     };

test/test.js

@@ -3971,17 +3971,18 @@
       deepEqual(_.dropWhile(objects, 'b'), objects.slice(2));
     });
 
-    test('should return a wrapped value when chaining', 2, function() {
+    test('should work in a lazy chain sequence', 3, function() {
       if (!isNpm) {
         var wrapped = _(array).dropWhile(function(num) {
           return num < 3;
         });
 
-        ok(wrapped instanceof _);
         deepEqual(wrapped.value(), [3, 4]);
+        deepEqual(wrapped.reverse().value(), [4, 3]);
+        strictEqual(wrapped.last(), 4);
       }
       else {
-        skipTest(2);
+        skipTest(3);
       }
     });
 
@@ -4856,17 +4857,18 @@
       deepEqual(_.takeWhile(objects, 'b'), objects.slice(0, 2));
     });
 
-    test('should return a wrapped value when chaining', 2, function() {
+    test('should work in a lazy chain sequence', 3, function() {
       if (!isNpm) {
         var wrapped = _(array).takeWhile(function(num) {
           return num < 3;
         });
 
-        ok(wrapped instanceof _);
         deepEqual(wrapped.value(), [1, 2]);
+        deepEqual(wrapped.reverse().value(), [2, 1]);
+        strictEqual(wrapped.last(), 2);
       }
       else {
-        skipTest(2);
+        skipTest(3);
       }
     });