Update PDO.php

Solves #254 - added inTransaction to the PHP 5.3 stub. Copied from the PHP 5.4 stub.

Added a note based on the documentation to indicate that in PHP 5.3 this method did not conform to the documented behaviour (returned int instead of bool).
Update PDO.php

Fixed whitespace issue.
Merge pull request #262 from kander/patch-1

Update PDO.php