jogl: add missing @Override annotation in NewtCanvasAWT

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
jogl: simplify conditional that repeats test for isOnScreen

if (isOnscreen)
else if (!isOnScreen)

change to

if (isOnscreen)
else

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
jogl: do the clearGlobalFocusOwner() call on the AWT EDT in NewtCanvasAWT

Otherwise we can deadlock in the native focusrequest calls from the AWT thread,
see bug 879 for the details.

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
jogl: push other call to clearGlobalFocus to the AWT EDT

Follow-on to commit:
d544c839f6df10f20977c786a446833f3aa7ef13 (jogl: do the clearGlobalFocusOwner() call on the AWT EDT in NewtCanvasAWT)

Likely this won't hurt anything.

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>