Fixed root operator

For some reason I thought that negative exponents gave roots and
not fractional ones.

tree.go

@@ -311,8 +311,8 @@ func (operation *Operation) Solution () (solution int64, err error) {
 			if index == 0 {
 				solution = subSolution
 			} else {
-				solution = integerPower (
+				solution = integerRoot (
-					solution, subSolution * -1)
+					solution, subSolution)
 			}
 		}
 	case OpcodeModulo:
@@ -410,9 +410,6 @@ func integerPower (x, y int64) (result int64) {
 	if y == 0 {
 		result = 1
 		return
-	} else if y < 0 {
-		// FIXME: find some algorithm for the nth root of an integer
-		result = int64(math.Pow(float64(x), float64(y)))
 	}
 	
 	result = x
@@ -422,6 +419,12 @@ func integerPower (x, y int64) (result int64) {
 	return
 }
 
+func integerRoot (x, y int64) (result int64) {
+	// FIXME: find some algorithm for the nth root of an integer
+	result = int64(math.Pow(float64(x), 1 / float64(y)))
+	return
+}
+
 type IntegerLiteral struct {
 	parent *Operation
 	displayRadix int