Use table aliases for columns in SQL generated by WP_Date_Query.

The use of non-aliased column names (eg 'post_date' instead of 'wp_posts.post_date')
in WP_Date_Query causes SQL notices and other failures when queries involve
table joins, such as date_query combined with tax_query or meta_query. This
changeset modifies WP_Date_Query::validate_column() to add the table alias when
it can be detected from the column name (ie, in the case of core columns).

A side effect of this change is that it is now possible to use WP_Date_Query
to build WHERE clauses across multiple tables, though there is currently no
core support for the automatic generation of the necessary JOIN clauses. See

Props ew_holmes, wonderboymusic, neoxx, Viper007Bond, boonebgorges.
Fixes #25775.
Built from https://develop.svn.wordpress.org/trunk@29933


git-svn-id: http://core.svn.wordpress.org/trunk@29685 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Support date_query by user_registered in WP_User_Query.

Props ChriCo, nacin.
Fixes #27283.
Built from https://develop.svn.wordpress.org/trunk@29934


git-svn-id: http://core.svn.wordpress.org/trunk@29686 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Comment/post author in/not_in for `WP_Comment_Query`.

Props nofearinc, chriscct7.
Fixes #29885.
Built from https://develop.svn.wordpress.org/trunk@29935


git-svn-id: http://core.svn.wordpress.org/trunk@29687 1a063a9b-81f0-0310-95a4-ce76da25c4cd