Issue #2045931 by Sam152, joelpittet, LinL, Sutharsan, adsw12: Replace all module_exists() deprecated function calls.

Issue #1493108 by marcingy, Mike Wacker, sun, kbasarab, Berdir, Rok Žlender, cosmicdreams, alexpott: Convert logging and error settings to configuration system.

This reverts commit 9db1fddb.

Nate Lampton authored Oct 30, 2011 and catch committed Nov 01, 2011

Issue #22336 by quicksketch, scor, boombatower, and rfay. Move all core Drupal files under a core subdirectory.

- Patch #502190 by jhodgdon, stella, sun: hook implementation headers out of compliance with standards.

- Patch #634234 by jhodgdon, arianek, lisarex: better help for system module, syslog module, and simpletest module.

#600974 by effulgentsia, JohnAlbin, sun, and Damien Tournoud: Allow theme functions to take one argument without any hacks. NOTE: This is an API change in hook_theme().

- Patch #572618 by effulgentsia, pwolanin, sun: all theme functions should take a single argument. Code clean-up and performance improvement. Woot.

- Patch #245115 by kkaefer, John Morahan, JohnAlbin et al: after a long discussion we've decided to make the concatenation operator consistent with the other operators.