Revert "Issue #813540 by jbrown, chx: Fixed Comparisons involving NULL must never return true."

This reverts commit 06f31080c7281c8227d2556cd0807744e91c9fb5.
- Patch #1146088 by lyricnz: label always visible for table formatter.
Merge branch '7.x' of git.drupal.org:project/drupal into 7.x
- Patch #1366804 by TR: 'End of foo group' on a couple of API pages due to not following standards.
- Patch #1265946 by klausi, tstoeckler, dereine, aspilicious: DoS against core using a large number of OR search query terms.
- Patch #1258000 by chx, xjm, bfroehle: SelectQuery::countQuery() inappropriately removes SQL expressions.
- Patch #1373360 by sun: fatal error if optional Block module is not enabled.
Issue #1240256 by lyricnz, Akaoni, jenspeter: Fixed file_unmanaged_copy() Fails with Drupal 7.7+ and safe_mode() or open_basedir().
Issue #1375134 by xjm, sun: Fixed Random test failure in TaxonomyTermTestCase::testNodeTermCreationAndDeletion().
Issue #1371484 by makara: Fixed Private properties in abstract class DrupalCacheArray.
Issue #1050466 by xjm, makara, rhayun: Fixed The taxonomy index should be maintained in a node hook, not a field hook.
Issue #1349610 by bartlantz, jhodgdon: Make the subtopics of Field API link back to it.
Issue #1347890 by sven.lauer, xjm, jhogdon: Clean up API docs for file module.
Issue #1319904 by rc_100, xjm, jhodgdon: Clean up API docs for help module.
Issue #1366740 by patrickd: Fixed theme_progress_bar() should have more information about when to use function.
Issue #678594 follow-up by mlncn: Add clarifying comment to RDFa markup for file/image formatters.
Issue #1366232 by sun: Fixed drupalCreateUser() breaks if testing site/profile does not install Comment module.
Issue #1362920 by scor, oriol_e9g: Wrong sitename variable in system.api.php.
Issue #1345480 by chris.leversuch, rbayliss: Fixed node_load() does not document FALSE return value.
Issue #866292 by marcingy, ygerasimov, quicksketch, attiks, furamag: Fixed '0' not displayed as checkbox / radios options (nor as any element #title).