Address TODOs

To make sure that our binarySearch implementation meets the requirements of
the library, I added more tests for ol.geom.flat.interpolate.lineString, only
to find out that it does not handle line strings with repeated vertices
properly, regardless of what binarySearch implementation is used.

src/ol/geom/flat/interpolateflatgeom.js

@@ -15,6 +15,7 @@ goog.require('ol.array');
  * @return {Array.<number>} Destination.
  */
 ol.geom.flat.interpolate.lineString = function(flatCoordinates, offset, end, stride, fraction, opt_dest) {
+  // FIXME does not work when vertices are repeated
   // FIXME interpolate extra dimensions
   goog.asserts.assert(0 <= fraction && fraction <= 1,
       'fraction should be in between 0 and 1');