Some time ago support for conf.d was added but it is currently broken if
the package does not have an `init.fish` file, given that `require`
enumerates packages through a glob on the existence of `init.fish`.

This fixes this requirement by globbing both `init.fish` and `conf.d`
entries in the `OMF_PATH`. This does generate duplicated entries, but
given that `require` already protects against double requires, this
should be safe.