Honor *loaded-libs* as single source of truth

[borkdude]

When libraries do something like this:

https://github.com/weavejester/integrant/blob/32a46f5dca8a6b563a6dddf88bec887be3201b08/test/integrant/core_test.cljc#L102-L104

a namespace should be reloaded when it's required again.