Prevent registration of accounts under protected names

Certain account names like "security", "info", "admins", etc. shouldn't be registrable to avoid confusion. (That said, security has already been registered, by me as a sysadmin, to facilitate creation of the security-discuss mailing list. But sysadmins ought to be trusted not to misuse the name for other things, like posing security@ as a security contact address for the SRCF...)

Given that group account creation is subject to manual review, there is already a layer of prevention that should stop such names being taken. It would be better if the set of "reserved" account names is programmatically enforced by our systems, though.

首先跟踪 Python 库中的账户和组创建路径，并确定名称在哪里进行验证或强制执行人工审核。定义受保护名称的行为，包括如何处理现有的安全账户，并添加或更新测试，以表明保留名称无法注册，同时允许的账户仍可正常工作。