`safe` is something I threw in there as a temp fix to be able to continue to run if a plugin failed. For example, most of the languages plugins fail because I don't have the particular language installed, but white/black-list stuff didn't exist yet.

`force` is something I held onto from `require_plugin`, in anticipation of someone calling `refresh_plugins` or wanting to make a plugin run again (by default, each plugin runs once).