We now support independent selection and primary clipboards, and avoid
wiping clipboard on modifying its contents from the same owner. This fixes
most of the interaction issues with clipboard and selection.
Signed-off-by: Rob Bradford <rob@linux.intel.com>
This follows the approach used by the Quartz port - that of a separate
implementation matching GtkClipboard.
The simple clipboard tests in gtk3-demo function correctly but there are
almost certainly leaks and bugs.
