Extra join conditions fails with 1 value using IN condition

When using an IN operator, the code introduced in "Allow additional field-to-field conditions with the default views_join handler (1090432)" causes the clause to fail if only a single value is provided. This is due to a check that changes the value formatting from "(value)" to "value" but fails to change the operator from "IN" to "=". This is due to the code defaulting back to the join info setting at the end of the extra handler in "build_join()" method (views/include/handlers.inc".

$operator = !empty($info['operator']) ? $info['operator'] : '=';

The $info array must have the operator when forcing a single value array to scalar. See proposed patch.