GLDrawable: Expose getRequestedGLCapabilities() (Include to public API)

In certain cases, it is required to read the user requested capabilities
from places other than the user code.

Hence adding public method to GLDrawable interface.

This removes the need to cast to private GLDrawableImpl,
which included such method.
Bug 830 - Refine Heuristics for to query whether GLDrawableUtil.swapGLContextAndAllGLEventListener is safe: Add Accumulator Buffer bits
Bug 1039 - Specify behavior of GLEventListener Exceptions occurring while GLAutoDrawable processing [part-1]

Implements Specification as described on 'Bug 1039 Comment 1'
  <https://jogamp.org/bugzilla/show_bug.cgi?id=1039#c1>

TODO:
  - Offthread exception handler

++++

GLDrawableHelper is used in all GLAutoDrawable implementations
and for most operations.

GLAutoDrawable/GLDrawableHelper invoke(..) method:

- invoke(..) forwards a caught exception
  - if blocking, it forwards an exception
    happening within the passed GLRunnable(s).
    Here the exception is caught, printed
    and then thrown by invoke itself.

  - if non-blocking, an exception
    happening within the passed GLRunnable(s)
    will be thrown in the thread issuing it's execution,
    i.e. display() call.
    Here the exception is not caught and simply thrown
    by the GLRunnable.

GLAutoDrawable.destroy() -> GLDrawableHelper.disposeGL(..) method:

- disposeAllGLEventListener() being invoked by disposeGL(..),
  catches exception thrown by GLEventListener.dispose(..)
  and prints them to stderr.
  The first caught exception is re-thrown at the end as an GLException.

- disposeGL() catches re-thrown GLException by disposeAllGLEventListener()
  for GLEventListener.dispose(..)
  and re-throws it when operation is complete.

- disposeGL() catches an exception thrown at context destruction or release
  and re-throws it when operation is complete.
  An early exception at context.makeCurrent() is _not_ caught,
  since it is the first operation which simply shall unwind the stack.

GLAutoDrawable.display() -> GLDrawableHelper.invokeGLImpl(..) method:

- invokeGLImpl(..) for display() follows disposeGL() mechanism, i.e.
  it catches exception thrown at
  GLEventListener's init(..), reshape(..) and display(..) methods
  and re-throws it when operation is complete.

  It also catches an exception thrown at context release
  and re-throws it when operation is complete.
  An early exception at context.makeCurrent() is _not_ caught,
  since it is the first operation which simply shall unwind the stack.

++++

None of the above thrown exception shall be caught and suppressed
on the caller side.

If an operation must be completed while an exception is caught,
it shall be cached and re-thrown after the operations.

In case multiple exception at multiple places are caught within
an operation, they all shall be cached and the first one
shall be re-thrown.

In case of multiple exception from the same place,
i.e. a loop through all GLEventListener,
the first shall be cached and re-thrown after operation is completed.

It has to be determined, whether we like to dump the exceptions,
especially the ones who get suppressed in case of multiple exceptions.