Loosened checks for PHPCPDTask and PHPLocTask

Currently, phing fails if the relevant include files are not found for the PHPCPDTask and PHPLocTask. This doesn't work very well when trying to use PHPCPD and PHPLOC from the Composer vendor directory.

I changed the code to not require these includes to succeed, but rather only to require that the relevant classes exist.

Interestingly, on my installation these includes are not needed at all:
@include_once('SebastianBergmann/PHPCPD/autoload.php');
@include_once('PHPCPD/Autoload.php');