Problem: the `load=true` in `vim.pack.add()` means that `:packadd` is
executed even during startup. This leads to force source of 'plugin/',
which breaks the intended loading order (`:h load-plugins`) and
results into sourcing them twice. This also makes it ignore
`--noplugin` argument.
Using `:packadd!` during startup is more appropriate, while `:packadd`
afterwards is still more favorable to actually force 'plugin/' source
(as there is no pre-defined mechanism that will load them later).
Solution: have `load=false` default during startup, `true` - afterwards.
b337c6e0fc