use influxdb aliases to distinguish between multiple columns

Currently if you have multiple values in a single series, grafana will use the aggregation function for the series name due to the default way influxdb returns column names. This PR alters the InfluxDB query (in a non-backwards compatible fashion sadly, requires InfluxDB 0.5.0rc3 or greater for column aliasing) to return the column name as [[column]]_[[func]] so the columns can be distinguished from each other if using the same aggregation function.