Allow whitelisting multiple nicks and idents

This change allows you to put nickname and ident patterns inside ldapwhitelist
tags, similarly to how IPs are currently whitelisted with the cidr attribute.

This lets you supply multiple nickname patterns to whitelist (vs allowpattern,
which only allows one), as well as allowing whitelisting based on ident
instead (which is most useful when you have userfield set to use the ident
instead of nickname for ldap searches).

Example usage:

    <ldapwhitelist nick="Guest*">
    <ldapwhitelist nick="*Bot">
    <ldapwhitelist ident="testing">