removed superfluous admin db check #367
made loadPlugin and unloadPlugin able to modify colls #367
gave PluginHandle a destructor so it's exception-safe #367
changed Loader's load and unload to manage local.system.plugins #367

The local.system.plugins collection will store info about loaded plugins
and we'll be able to look there to know how to automatically load them
on startup next time.
deleted listPlugins command #367

This information is now available by just querying local.system.plugins.