phpdoc and cleanup of deprecated $table globals

[nacin]

Trivial patch adds some phpdoc does slight cleanup. Alternatively, these globals can probably be removed at this point, as any plugin that uses them is doing it wrong. (Or is older than time.)

[dd32]

$tablecategories = $wpdb->categories;

My vote would be to remove those 2 items at least.. They're useless now.

As for the rest of the $table* vars.. I'd be tempted to say get rid of those too.. They need to be cleaned up at some point.

[nacin]

Two more patches with the alternatives. Machete or scalpel, take your pick.

[hakre]

For 3.0 we should not fear to break things, so just drop those (if you ask me). I've reviewed current trunk if those vars are used anywhere else and next to depreceated.php those do not appear anywhere.

In case you need a handy regex to smell them:
\$table(posts|users|categories|post2cat|comments|options|postmeta)

[nacin]

(In [13229]) Introduce wpdb::tables() to fetch table names on a global or blog scope. Remove very old and long deprecated $table{table} globals, fixes #11614. See #12083