[gh-518] Upgrade Drupal Core to 7.18

CHANGELOG.txt

includes/bootstrap.inc

includes/file.inc

modules/aggregator/aggregator.info

modules/aggregator/tests/aggregator_test.info

modules/block/block.info

modules/block/tests/block_test.info

...block/tests/themes/block_test_theme/block_test_theme.info

modules/blog/blog.info

modules/book/book.info

modules/color/color.info

modules/comment/comment.info

modules/contact/contact.info

modules/contextual/contextual.info

modules/dashboard/dashboard.info

modules/dblog/dblog.info

modules/field/field.info

...es/field/modules/field_sql_storage/field_sql_storage.info

modules/field/modules/list/list.info

modules/field/modules/list/tests/list_test.info