Convert an X11 timestamp into a user action time as used in Telepathy.
This also works for the timestamps used by GDK 2, GDK 3 and Clutter 1.0; it may or may not work with other toolkits or versions.
| x11_time |
an X11 timestamp, or 0 to indicate the current time |
|
a nonzero Telepathy user action time, or |