Spread requests over all available buckets

Smaller requests are quicker and allows requesting timed-out cells more quickly. by @ah42
iitc-project/ingress-intel-total-conversion#1131
#2

code/map_data_request.js

@@ -376,11 +376,12 @@ window.MapDataRequest.prototype.processRequestQueue = function(isFirstPass) {
   var requestBuckets = this.MAX_REQUESTS - this.activeRequestCount;
   if (pendingTiles.length > 0 && requestBuckets > 0) {
 
+    var requestBucketSize = Math.min(this.NUM_TILES_PER_REQUEST, Math.max(5, Math.ceil(pendingTiles.length / requestBuckets)));
     for (var bucket=0; bucket < requestBuckets; bucket++) {
 
       // if the tiles for this request have had several retries, use smaller requests
       // maybe some of the tiles caused all the others to error? no harm anyway, and it may help...
-      var numTilesThisRequest = Math.min(this.NUM_TILES_PER_REQUEST,pendingTiles.length);
+      var numTilesThisRequest = Math.min(requestBucketSize, pendingTiles.length);
 
       var id = pendingTiles[0];
       var retryTotal = (this.tileErrorCount[id]||0);