pudl::insert accepts true for update clause

When passing "TRUE" to the update clause of pudl::insert(), update uses
the same data as the main data clause for insert.

In effect, pudl::insert('table', $data, true, $data) and
pudl::insert('table', $data, true, true) are equal

This enables code such as:
pudl::insert('table', array(
'a'=>1,
'b'=>2,
'c'=>3,
), true, true)