drawAsInfinite should not cause y-axis expansion

We are using a metric as a marker whenever deployments happen. That marker happens to have a low value (say, 1.0). However, we render that metric using the drawAsInfinite function. We don't really care about the value of this metric, only the time the metric was observed.

Unfortunately, a consequence of using low values for our deployment metric is that graphs containing other metrics with constant, high values (memory use for example) are forced to contain the entire Y axis. The same problem would happen if the marker metric contained high values and was used on a graph containing metrics with very low values (response times for example).

The drawAsInfinite function should prevent its series values from affecting the scale of the y-axis.

An example URL would look something like:

http://graphite/render?target=drawAsInfinite(deploy.total)&target=cache.size&from=-1w