clipboard: fwd owner-change event from GtkClipboard

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>

Conflicts:
	libgpaste/core/gpaste-clipboard.c
settings: use g_clear_object

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>
clipboards-manager: port to owner-change signal

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>

Conflicts:
	libgpaste/core/gpaste-clipboards-manager.c
clipboards-manager: fix warnings

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>
update NEWS

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>
remove traces of xfixes

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>