Fix ignored_packages setting getting changed at startup if default pa…

…ckages have been extracted

If the default packages aren't in a `.sublime-package` file then on
startup the `"ignored_packages"` setting would always be set to `[]`.

Primarily this fixes our development environment where we don't use any
`.sublime-package` files, but presumably there are also people who've
extracted these folders (as unwise as that may be).

package_control/package_manager.py

@@ -797,6 +797,7 @@ def list_default_packages(self):
         """
 
         packages = set(list_sublime_package_files(sys_path.default_packages_path()))
+        packages |= set(list_sublime_package_dirs(sys_path.default_packages_path()))
         packages -= {'User'}
         return packages