Plugin loader tries to load every file in the plugin directory, not every module

[rsalmond]

While developing a plugin I discovered that the plugin loader system is recursively calling imp.load_module() on every file it finds under the PLUGIN_PATH, not every directory / module. Because of this __init__.py is not always parsed prior to other code in the module.

I'm cutting an issue instead of a PR because I can't think of a situation where doing module imports rather than file imports would break something but I want to get some second opinions because maybe I'm just not very imaginative.

[BrianGallew]

The only negative is that if you import a module you must avoid name collisions. That's not usually a big deal, but can occasionally bite people. One benefit is that it would let plugins reference each other more easily. It's probably more because of my poor coding skills, but I occasionally end up in situations where I have two separate plugins, each with distinct configs, that would really like to reference each other. Sure, you can use @route() to provide a kind of back channel, but I'm not a fan of that.