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.

I also added two additional tasks (<include> and <require>). I believe that these tasks can be used instead of the <includepath> task. In my use case, when using Composer, it is easier for me to do <include file="vendor/autoload.php"> than to use "includepath" multiple times for many of the PHP tools (phpmd, phpcpd, etc.).