Select the buffer containing the current tags table.
If optional arg is a string, visit that file as a tags table.
If optional arg is t, visit the next table in `tags-table-list'.
If optional arg is the atom `same', don't look for a new table;
just select the buffer visiting `tags-file-name'.
If arg is nil or absent, choose a first buffer from information in
`tags-file-name', `tags-table-list', `tags-table-list-pointer'.
Returns t if it visits a tags table, or nil if there are no more in the list.
(fn &optional CONT)