Followup to previous changes:
* Use camel case, as PDO uses a camel case OO API.
* Use &$var instead of &$bind_var or &$param.
* Use $column instead of $index. We have cases (both inside PDO
and in other DB exts) where columns can also be represented as
strings, so $column is the safer generic name.
Closes GH-6272.
0f3698173e