PluginManager: An extensible plugin management API for Rails

I've begun implementing an API for installing, updating and removing
plugins. This will allow for pluggable plugin managers, e.g. to
support other version control systems than those built into Rails.

I haven't got a lot of expertise in this area, so if anyone has some
good comments on the design/approach, please say so.

My current design is this:

A plugin manager, e.g. GitPluginManager, inherits from
PluginManager::Base. It can override #install, #update and #remove. It
hooks into a URI scheme (e.g. "git://...") by calling
PluginManager.add_plugin_manager(uri_scheme, manager).

PluginManager.install(uri[, options]) installs the plugin identified
by the URI. Behind the scene, a suitable plugin manager is found, and
its #install method is called.

PluginManager.update(name[, options]) updates the named plugin (e.g.
"acts_as_awesome"). I have not begun work on this yet.

PluginManager.remove(name[, options]) removes the named plugin. Behind
the scenes, PluginManager finds out which plugin manager has installed
the plugin using heuristics. So far, I've got support for removing
plain directories and git submodules (the latter needs extra cleanup
in .gitmodules). Subversion externals is planned.

The progress will be tracked in Lighthouse[1], and the code is
residing in a GitHub branch[2].

Again, all comments are welcome.

Cheers,
Daniel Schierbeck

[1] <http://rails.lighthouseapp.com/projects/8994-ruby-on-rails/
tickets/1436>
[2] <http://github.com/dasch/rails/tree/plugin-manager>