Client authentication

Functions:

There are four client authentication functions:

client_ok() returns true or false, depending on whether the IP address is in one of two files. Typically, the first file is a list of people with permanent IP addreses, together with their names. The second file is intended to be maintained by other software to allow for people dialling in who have dynamically assigned IP addresses.
client_realname() returns the real name of the client from the files.
client_nickname() returns a nickname of the client from the files.
userlist() returns an array containing the real names of all authorized users.

The datafiles are human-readable ascii databases.

Comments are begun with a pound sign (#) and continue to the end of the line.
The first column (up to a space or tab) is the IP address or machine name. You may want to have both, as some browsers in some situations supply a numerical IP address, and some can figure out a name. No fancy matching is done - the software just compares whatever the browser produces to the entries in the first column.
Everything else is a name. If there is something in parentheses, it is treated as the nickname. It is useful if the realnames are acceptable to other software, like Post, for instance.
Strictly speaking, things in parentheses are removed for client_fullname(). For client_nickname(), everything before the parentheses is replaced by the contents of the parentheses.
```
# comment here
gpkpc.research.att.com Gregory(Greg) Kochanski
tompc.research.att.com J. Thomas Snead(Bigshot)
192.11.66.1 Someone else #and a comment
```