Handle long values passed to ZenHub's writeRRD via XML-RPC

[chris]

The XML-RPC standard does not support passing long values. There are many times where we're going to need to pass long values to writeRRD (in the "value" parameter). This often appears in ZenJMX when reporting values for CPU ticks that Java has made.

We should update ZenHub's RRDImpl to convert the value to a long if the datapoint type is a counter or derive. Then XML-RPC clients can safely pass the long value as a String, double, float, or some other variant that has sufficient precision to represent such a long value.

[chris]

(In [7243]) fixes #2218: convert the value to a long if the rrd data type is a
counter or a derive. should we also convert on absolute?

[chris]

(In [7244]) refs #2218: pass integer based datapoint values as strings

[marc]

r7446 Patches r7243 r7244 to 2.1.x branch