Issue #1425868 by ELC, lort, greg.harvey, David_Rothstein: Fixed duplicate entry of theme primary key in system table on Drupal 6.24 when updating using drush.

Issue #147000 by Berdir, Dave Reid, pwolanin, pillarsdotnet, TR, jbrauer, dstol: rework module_rebuild_cache() and system_theme_data() to support locking, so that concurrent requests will not corrupt the data; fixes an issue where themes got disabled occasionally

Issue #480082 by pp: add previously undocumented variables in system_send_email_action_form()'s message field description

Issue #632080 by donquixote, mathieu, jonhattan, andypost: clone return values from _system_theme_data(), so modules careless about lack of object copies will not overwrite the system level cached values

#147000 by pwolanin, mikeytown2, et. al.: avoid multiple, parallel rebuildings of module and theme data

#764234 by yan_nick, Zoltan Balogh and myself: backport width of user filter labels in admin forms; better fit for some translations

#245990 by David_Rothstein, Pedro Lozano, andypost: do not follow any redirections in system_check_http_request() since we only need data on whether HTTP requests worked at all

#767408 by hunmonk: copy semaphore site creation to update_fix_d6_requirements() to solve issues upgrading from any version of Drupal 5

#764548 by Dave Reid, sun: backport hiding of hidden modules on the modules page, so if projects include hidden modules for testing, those will not confuse users

#629958 by jhodgdon, rdrh555: improve documenatation consistency and mention the node variable in page.tpl.php

#495956 by cafuego, sun, andypost, Josh Waihi, axyo: do not assume that the database will insert role numbers or filter format indexes in a specific way

#358315 by neochief, Damien Tournoud, andypost: drupal_lookup_path() does not respect path alias ordering when older aliases are retained