Merge pull request #306 from ParsePlatform/richardross.collectdirtychildren.deadlock

Fixed deadlock in -collectDirtyChildren:

Author: richardjrossiii

Parse/PFObject.m

@@ -263,6 +263,7 @@ + (void)collectDirtyChildren:(id)node
 
     } else if ([node isKindOfClass:[PFObject class]]) {
         PFObject *object = (PFObject *)node;
+        NSDictionary *toSearch = nil;
 
         @synchronized ([object lock]) {
             // Check for cycles of new objects.  Any such cycle means it will be
@@ -288,18 +289,19 @@ + (void)collectDirtyChildren:(id)node
             // Recurse into this object's children looking for dirty children.
             // We only need to look at the child object's current estimated data,
             // because that's the only data that might need to be saved now.
-            [self collectDirtyChildren:object->_estimatedData.dictionaryRepresentation
-                              children:dirtyChildren
-                                 files:dirtyFiles
-                                  seen:seen
-                               seenNew:seenNew
-                           currentUser:currentUser];
-
-            if ([object isDirty:NO]) {
-                [dirtyChildren addObject:object];
-            }
+            toSearch = [object->_estimatedData.dictionaryRepresentation copy];
         }
 
+        [self collectDirtyChildren:toSearch
+                          children:dirtyChildren
+                             files:dirtyFiles
+                              seen:seen
+                           seenNew:seenNew
+                       currentUser:currentUser];
+
+        if ([object isDirty:NO]) {
+            [dirtyChildren addObject:object];
+        }
     } else if ([node isKindOfClass:[PFFile class]]) {
         PFFile *file = (PFFile *)node;
         if (!file.url) {