make rebaseline_server client check schema version number

gm/rebaseline_server/static/loader.js

 /*
  * Loader:
  * Reads GM result reports written out by results.py, and imports
  * them into $scope.extraColumnHeaders and $scope.imagePairs .
  */
 var Loader = angular.module(
     'Loader',
     ['ConstantsModule']
 );
 
@@ skipping 71 matching lines @@
               dataHeader[constants.KEY__HEADER__TIME_NEXT_UPDATE_AVAILABLE] -
               dataHeader[constants.KEY__HEADER__TIME_UPDATED];
           var timeNow = new Date().getTime();
           var timeToReload = timeNow + reloadDelayInSeconds * 1000;
           $scope.loadingMessage =
               "Server is still loading results; will retry at " +
               $scope.localTimeString(timeToReload / 1000);
           $timeout(
               function(){location.reload();},
               timeToReload - timeNow);
+        } else if (dataHeader[constants.KEY__HEADER__SCHEMA_VERSION] !=
+                   constants.REBASELINE_SERVER_SCHEMA_VERSION_NUMBER) {
+          $scope.loadingMessage = "ERROR: Got JSON file with schema version "
+              + dataHeader[constants.KEY__HEADER__SCHEMA_VERSION]
+              + " but expected schema version "
+              + constants.REBASELINE_SERVER_SCHEMA_VERSION_NUMBER;
         } else {
           $scope.loadingMessage = "Processing data, please wait...";
 
           $scope.header = dataHeader;
           $scope.extraColumnHeaders = data[constants.KEY__EXTRACOLUMNHEADERS];
           $scope.imagePairs = data[constants.KEY__IMAGEPAIRS];
           $scope.imageSets = data[constants.KEY__IMAGESETS];
           $scope.sortColumnSubdict = constants.KEY__DIFFERENCE_DATA;
           $scope.sortColumnKey = constants.KEY__DIFFERENCE_DATA__WEIGHTED_DIFF;
 
@@ skipping 683 matching lines @@
      */
     $scope.getImageDiffRelativeUrl = function(imagePair) {
       var before =
           imagePair[constants.KEY__IMAGE_A_URL] + "-vs-" +
           imagePair[constants.KEY__IMAGE_B_URL];
       return before.replace(/[^\w\-]/g, "_") + ".png";
     }
 
   }
 );