[mrtg] Configuring MRTG/rrdtool with <1 minute intervals

[Steve Shipway]

> 2.15.0.  From the changelog:
>       * mrtg running with rrdtool can now do sub-minute resolution if
>         the interval is specified like that: 0:30

Routers2.18beta6 now supports this new format of specifying Interval.  No graph smaller than 6hours, though.

Actually, it appears that routers2 will work with this format of interval definition already - it will just ignore the seconds part.  Since the Interval is only used to see if it should enable the 6Hour graphs, this is fine.

Steve