mod_adhoc_dataforms_demo: Fix duplicate field prevention It's supposed to only include each type of form field once per form at most but it didn't note which fields it had added already. No idea what the probability was anyways, probably pretty low.

This module lets you block connections to any remote servers not on a
whitelist.

``` {.lua}
s2s_whitelist = {
    "example.org",
}
```