The rrdtool -t option is only available for 1.6.0+
The rrdtool -t option is only available for 1.6.0+

Caused all data to go "missing" with earlier rrdtool versions.

Was removed in commit d5f1ebdbd273ebe1a2a870186150a1d6a5326b58,
and then re-added in 702bc04269399b466ef4666b79ebf2de87507e5d.

Add some version checking, so that it stops breaking like that.

Note that rrdtool 1.5.x never outputs any timestamps, so there
we have to _calculate_ the timestamp based on current data row.

ganglia/ganglia-web,ganglia/ganglia-web,ganglia/ganglia-web,ganglia/ganglia-web,ganglia/ganglia-web