aggregate: function should register all short forms as an alias

 * This allows groupByNode/groupByNodes to call all available summarizer functions

Fixes #466

expr/functions/aggregate/function.go

@@ -24,6 +24,11 @@ func New(configFile string) []interfaces.FunctionMetadata {
 	for _, n := range []string{"aggregate"} {
 		res = append(res, interfaces.FunctionMetadata{Name: n, F: f})
 	}
+
+	// Also register aliases for each and every summarizer
+	for _, n := range consolidations.AvailableSummarizers {
+		res = append(res, interfaces.FunctionMetadata{Name: n, F: f})
+	}
 	return res
 }
 
@@ -36,7 +41,11 @@ func (f *aggregate) Do(e parser.Expr, from, until int64, values map[parser.Metri
 
 	callback, err := e.GetStringArg(1)
 	if err != nil {
-		return nil, err
+		if e.Target() == "aggregate" {
+			return nil, err
+		} else {
+			callback = e.Target()
+		}
 	}
 
 	// TODO: Implement xFilesFactor

expr/functions/diffSeries/function.go

@@ -2,12 +2,13 @@ package diffSeries
 
 import (
 	"fmt"
+	"math"
+	"strings"
+
 	"github.com/go-graphite/carbonapi/expr/helper"
 	"github.com/go-graphite/carbonapi/expr/interfaces"
 	"github.com/go-graphite/carbonapi/expr/types"
 	"github.com/go-graphite/carbonapi/pkg/parser"
-	"math"
-	"strings"
 )
 
 type diffSeries struct {