Add asynchronous API for fetching current user.

Author: nlutsenko

Parse/PFUser.h

@@ -45,6 +45,13 @@ typedef void(^PFUserLogoutResultBlock)(NSError *_Nullable error);
  */
 + (nullable instancetype)currentUser;
 
+/**
+ *Asynchronously* loads the currently logged in user from disk and returns a task that encapsulates it.
+
+ @return The task that encapsulates the work being done.
+ */
++ (BFTask<__kindof PFUser *> *)getCurrentUserInBackground;
+
 /**
  The session token for the `PFUser`.
 

Parse/PFUser.m

@@ -780,8 +780,11 @@ + (NSString *)parseClassName {
 }
 
 + (instancetype)currentUser {
-    PFCurrentUserController *controller = [[self class] currentUserController];
-    return [[controller getCurrentObjectAsync] waitForResult:nil withMainThreadWarning:NO];
+    return [[self getCurrentUserInBackground] waitForResult:nil withMainThreadWarning:NO];
+}
+
++ (BFTask<__kindof PFUser *> *)getCurrentUserInBackground {
+    return [[[self class] currentUserController] getCurrentObjectAsync];
 }
 
 - (BOOL)_current {