Adds *hostname* to the list of remote hosts allowed to execute the function *fname*.
## Access control
Access control is implemented by way of an "allow" list and a "deny" list. Any function lacking both lists will default to the function being available to all hosts.
Any entries in the 'allow' list for a function will disable access for any but those in the allow list.
Entries in the 'deny' list will result in the hosts in said list being denied, but other hosts are allowed. This will not override the 'allow' list.