Debug: Add "Last spoke" timestamp
Debug: Add "Last spoke" timestamp

This is just a hack to facilitate quickly finding instances in debug.out
files where Orca failed to say anything for a long time, e.g. due to an
event flood or AT-SPI2 failing to send over any events.

GNOME/orca,GNOME/orca,GNOME/orca,GNOME/orca