Fix DbFactory

[Gillingham]

The filename is PdoDB.php so we need to handle that, and use an uppercase 'DB' when calling the className. Alternatively, the PdoDB file could be renamed, but I'm sure which you would prefer.

[linc]

Thank you!

Note for future reference: The issue here is that while classes are case-insensitive, the autoloader can be case sensitive when the class hasn't loaded yet because file_exists() is case-sensitive. I obviously never hit that scenario in my testing.