Strict address enforcement mistakenly treats user bans as IP bans

[A248]

When STRICT enforcement is configured, a user ban is enforced more stringently than it should be, as if it were an IP ban.

No such problem exists under LENIENT or NORMAL strictness.

For backwards compatibility reasons, retroactively changing the behavior of STRICT enforcement is unwise. Thus:

• We will adjust the documentation of STRICT enforcement to match the de-facto behavior.
• A new enforcement setting, in between NORMAL and STRICT, will achieve the originally-intended behavior of STRICT.