added OSX convenience method

git-svn-id: svn+ssh://svn.gna.org/svn/gnustep/libs/base/trunk@36966 72102866-910b-0410-8b05-ffd578937521

Source/NSThread.m

@@ -1303,6 +1303,15 @@ GSRunLoopInfoForThread(NSThread *aThread)
           waitUntilDone: aFlag
                   modes: commonModes()];
 }
+
+- (void) performSelectorInBackground: (SEL)aSelector 
+                          withObject: (id)anObject
+{
+  [NSThread detachNewThreadSelector: aSelector
+                           toTarget: self
+                         withObject: anObject];
+}
+
 @end
 
 /**