Support --allow-incompatible-update in meteor list

Undocumented flag.  This is one of those cases that is rare but may
come up, because `meteor list` runs the version solver (and writes
.meteor/versions).  For example, it may come up if you run `meteor 
list` with PACKAGE_DIRS and then without (or vice versa).  You'll
get a message that says to pass --allow-incompatible-update, so we
must support it.

tools/commands-packages.js

@@ -1095,11 +1095,13 @@ main.registerCommand({
   name: 'list',
   requiresApp: true,
   options: {
+    'allow-incompatible-update': { type: Boolean }
   },
   catalogRefresh: new catalog.Refresh.OnceAtStart({ ignoreErrors: true })
 }, function (options) {
   var projectContext = new projectContextModule.ProjectContext({
-    projectDir: options.appDir
+    projectDir: options.appDir,
+    allowIncompatibleUpdate: options['allow-incompatible-update']
   });
   main.captureAndExit("=> Errors while initializing project:", function () {
     projectContext.prepareProjectForBuild();