Add asynchronous API for fetching current installation.

Author: nlutsenko

Parse/PFInstallation.h

@@ -44,14 +44,23 @@ PF_TV_UNAVAILABLE PF_WATCH_UNAVAILABLE @interface PFInstallation : PFObject<PFSu
 /**
  Gets the currently-running installation from disk and returns an instance of it.
 
- If this installation is not stored on disk, returns a `PFInstallation`
- with `deviceType` and `installationId` fields set to those of the
- current installation.
+ If this installation is not stored on disk this method will create a new `PFInstallation`
+ with `deviceType` and `installationId` fields set to those of the current installation.
 
  @result Returns a `PFInstallation` that represents the currently-running installation.
  */
 + (instancetype)currentInstallation;
 
+/**
+ *Asynchronously* loads the currently-running installation from disk and returns an instance of it.
+
+ If this installation is not stored on disk this method will create a new `PFInstallation`
+ with `deviceType` and `installationId` fields set to those of the current installation.
+
+ @result Returns a task that incapsulates the current installation.
+ */
++ (BFTask<__kindof PFInstallation *> *)getCurrentInstallationInBackground;
+
 ///--------------------------------------
 #pragma mark - Installation Properties
 ///--------------------------------------

Parse/PFInstallation.m

@@ -132,8 +132,11 @@ + (PFQuery *)query {
 ///--------------------------------------
 
 + (instancetype)currentInstallation {
-    BFTask *task = [[self _currentInstallationController] getCurrentObjectAsync];
-    return [task waitForResult:nil withMainThreadWarning:NO];
+    return [[self getCurrentInstallationInBackground] waitForResult:nil withMainThreadWarning:NO];
+}
+
++ (BFTask<__kindof PFInstallation *> *)getCurrentInstallationInBackground {
+    return [[self _currentInstallationController] getCurrentObjectAsync];
 }
 
 ///--------------------------------------