speed up legacy springboarding

after the first time you springboard to a legacy release, don't refresh
the catalog before springboarding

tools/main.js

@@ -776,6 +776,17 @@ Fiber(function () {
   }
 
   if (releaseName !== undefined) {
+    // First, if we know just by looking at our disk that this is a legacy
+    // pre-0.9.0 release, springboard to it immediately, before calling
+    // release.load (which will refresh the catalog because the release
+    // presumably doesn't exist on the new server, and this is a slow
+    // operation).
+    if (warehouse.releaseExistsInWarehouse(releaseName)) {
+      var manifest = warehouse.ensureReleaseExistsAndReturnManifest(
+        releaseName);
+      oldSpringboard(manifest.tools);
+    }
+
     try {
       var rel = release.load(releaseName);
     } catch (e) {

tools/warehouse.js

@@ -124,6 +124,13 @@ _.extend(warehouse, {
     return fs.existsSync(warehouse.getToolsDir(version));
   },
 
+  releaseExistsInWarehouse: function (version) {
+    var releasesDir = path.join(warehouse.getWarehouseDir(), 'releases');
+    var releaseManifestPath = path.join(releasesDir,
+                                        version + '.release.json');
+    return fs.existsSync(releaseManifestPath);
+  },
+
   _calculateNewPiecesForRelease: function (releaseManifest) {
     // newPieces.tools and newPieces.packages[PACKAGE] are either falsey (if
     // nothing is new), or an object with keys "version" and bool