based on SteadyTime (which uses the CLOCK_MONOTONIC).
This timer is not influenced by time jumps of the system time,
so ideal for things like periodic checks of timeout/heartbeat, etc...

This is a bit of a hack, since up to boost version 1.61 the time of the steady clock is always converted to system clock,
which is then used for the wait... which obviously doesn't help if we explicitly want the steady clock.

So as a workaround, include the backported versions of the boost condition variable if boost version is not recent enough.

not sure if this is only need in my case on ROS indigo...

…d if needed

to avoid the typeid check and make really sure the correct boost condition wait_until implementation is used

This reverts commit f62a3f2.

The important change is the minimum version for the dependency on rostime to ensure the version contains SteadyTime.

The other changes are mostly spaces.