Issue #1269742 by katbailey, beejeebus, pwolanin, g.oechsler, ksenzee: Make path lookup code into an pluggable class.

Issue #1711070 by kid_icarus, tim.plunkett, xjm, droplet, zendoodles and cam8001: Convert tests to use ::$modules property instead of parent::setUp($modules).

- Patch #1696902 by sun, larowlan, cosmicdreams, heyrocker, tobiasb: Convert forum_admin_settings() to new configuration system.