Changes

AWT GLCanvas: More strict GLDrawable realization [on AWT-EDT], skip if creation is not possible on AWT-EDT.

The Intel HD3000 OpenGL driver on Windows will deadlock @ SwapBuffers in case the drawable is created
on a thread other than the window owner thread.

We are aware of such possibilities, nevertheless the AWTEDTExecutor.singleton.invoke(..)
allowed to execute the runnable in case it cannot be invoked on AWT-EDT.
The latter is the case if the current thread is not the AWT-EDT _and_ is holding the AWT tree-lock.

With GlueGen commit 0b43b43f889ad7fc220942b0076e2001ca3cf13f, the invoke method now consumes
an argument allowing to restrict the execution to AWT-EDT only.

In such case, the drawable will be realized at a later time from the AWT-EDT.

Such a situation could be triggered if a Frame's setVisible(true)
is not issued from the AWT-EDT, as it should be!
However, to relax such use cases - we better recognize such possible dealock and avoid it.