Add experimental "show grid users online" console command to show grid users online from a standalone/robust instance.

This is not guaranteed to be accurate since users may be left "online" in certain situations.
For example, if a simulator crashes and they never login/logout again.
To counter this somewhat, only users continuously online for less than 5 days are shown.
Merge branch 'master' of ssh://opensimulator.org/var/git/opensim
Fix logic errors in "show grid users online" console command which didn't actually filter out users shown continuously online for more than 5 days

Remove confusion in command output.
minor simplification of some unix date functions in Util.  No functional change.