timedatectl: work with old timedated

Which does have TimeUSec. Should we specifically check for this method
instead of assuming time=0 means it doesn't exist?

Before:
shawn@debian-T61:~/git/systemd$ ./timedatectl
      Local time: Wed 1969-12-31 16:00:00 PST
  Universal time: Thu 1970-01-01 00:00:00 UTC
        RTC time: n/a
        Timezone: America/Los_Angeles (PST, -0800)
     NTP enabled: n/a
NTP synchronized: no
 RTC in local TZ: no
      DST active: no
 Last DST change: DST ended at
                  Sun 1969-10-26 01:59:59 PDT
                  Sun 1969-10-26 01:00:00 PST
 Next DST change: DST begins (the clock jumps one hour forward) at
                  Sun 1970-04-26 01:59:59 PST
                  Sun 1970-04-26 03:00:00 PDT

After:
shawn@debian-T61:~/git/systemd$ ./timedatectl
      Local time: Wed 2013-12-11 14:03:21 PST
  Universal time: Wed 2013-12-11 22:03:21 UTC
        RTC time: n/a
        Timezone: America/Los_Angeles (PST, -0800)
     NTP enabled: n/a
NTP synchronized: no
 RTC in local TZ: no
      DST active: no
 Last DST change: DST ended at
                  Sun 2013-11-03 01:59:59 PDT
                  Sun 2013-11-03 01:00:00 PST
 Next DST change: DST begins (the clock jumps one hour forward) at
                  Sun 2014-03-09 01:59:59 PST
                  Sun 2014-03-09 03:00:00 PDT
bus: enforce endianess and marshalling for messages we send
bus: always pass valid timeout to kdbus