Backport for [JDK-8131151] Pressing ESC in a nested alert closes self and parent alert

[Werner Lehmann]

Hi,

since there seems to be an opportunity to have fixes backported to 8, 
I'd like to ask for a backport of the fix for

[JDK-8131151] Pressing ESC in a nested alert closes self and parent alert
https://bugs.openjdk.java.net/browse/JDK-8131151

Looks as if the fix is pretty simple. Without this we seem to be forced 
to disallow closing dialogs with escape key because the following 
yes/no/cancel alert would be dismissed right away from the same 
keypress. Admittedly, it is not critical in any way but the backport 
risk should be low.

Rgds
Werner