Update Pdo.php

[multiwebinc]

Allow users to provide an already existing connection instead of forcing a new one to be created for phpsec. The only thing I changed was the constructor, but for some reason github thinks I changed the whole file. I'm assuming it's an indentation issue. I'm new to github and I don't know how to edit this thing, so maybe someone else could just copy and paste the changed lines from the constructor if you feel it's useful.

[woutervanvliet]

Why does $loc remain unused and does this constructor introduce a new parameter $table?

Perhaps it's better to pass the table name through $loc as normal and make the third param in the constructor dual purpose (either additional connection options, or existing PDO instance). This would be more future-feature compatible.