<AWT Dev> [7u12] Review request for 7175707: [macosx] PIT: 8 b43 Not running on AppKit thread issue again

[Alexander Scherbatiy]

This is a direct backport of the fix from the JDK 8 to JDK 7u12

bug: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7175707
webrev: http://cr.openjdk.java.net/~alexsch/7175707/webrev.01

The nativeGetNSWindowDisplayID_AppKitThread can be invoked both from the 
AppKitThread and not from the AppKitThread.
The fix invokes the getNSWindowDisplayID_AppKitThread method on the 
AppKitThread in case if we are no on the AppKitThread.

The GetNSWindowDisplayID_AppKitThread method is renamed to 
getNSWindowDisplayID_AppKitThread.

Thanks,
Alexandr.