Note: In a previous commit, I began making inc/mod/auth.php more modular with the check_login() function. Including it does NOT check mod login by default anymore like it does on vichan. You have to call check_login(). I've finally included it in inc/functions.php. If you have any custom pages that use inc/mod/auth.php, just including functions.php is enough now.

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Also: backports 351375185e5 (early 404)

This allows pages like create.php to not include inc/mod/pages.php while still being able to use the mod auth functions (like generating salts and passwords)

Conflicts:
	inc/mod/auth.php
	inc/mod/pages.php

cache::get() returns null if the key wasn't found (at least when using
the Redis cache backend).