GPasteHistory: track only the biggest index

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>
GpasteHistory: fix max memory logic

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

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