Add an ol.coordinate.distance() helper method.

The method is a companion to {@link ol.coordinate.squaredDistance}.
The new method returns the Cartesian distance, instead of its square.

Conflicts:
	src/ol/coordinate.js

src/ol/coordinate.js

@@ -250,6 +250,16 @@ ol.coordinate.squaredDistance = function(coord1, coord2) {
 };
 
 
+/**
+ * @param {ol.Coordinate} coord1 First coordinate.
+ * @param {ol.Coordinate} coord2 Second coordinate.
+ * @return {number} Distance between coord1 and coord2.
+ */
+ol.coordinate.distance = function(coord1, coord2) {
+  return Math.sqrt(ol.coordinate.squaredDistance(coord1, coord2));
+};
+
+
 /**
  * Calculate the squared distance from a coordinate to a line segment.
  *