Refactor command code and add support for --help and --version.

utils/pub/package.dart

Index: utils/pub/package.dart
diff --git a/utils/pub/package.dart b/utils/pub/package.dart
index 8a672f82ab0cb56bb91e295f66907d1736ff22c8..8e621371591ac08f04df69a7343c5c017b5b35fc 100644
--- a/utils/pub/package.dart
+++ b/utils/pub/package.dart
@@ -46,7 +46,7 @@ class Package implements Hashable {
   /**
    * Reads and returns all of the packages this package immediately depends on.
    */
-  Future<Collection<Package>> loadDependencies() {
+  Future<Collection<Package>> loadDependencies(PackageCache cache) {
     return Futures.wait(dependencies.map((name) => cache.find(name)));
   }
 
@@ -55,7 +55,7 @@ class Package implements Hashable {
    * [Set] of all of the packages dependend on by this one, directly or
    * indirectly. This package is included in the result set.
    */
-  Future<Set<Package>> traverseDependencies() {
+  Future<Set<Package>> traverseDependencies(PackageCache cache) {
     final completer = new Completer<Set<Package>>();
     final packages = new Set<Package>();