Adapting "AbstractSniffUnitTest" to work with PHPCS 2.x

- unit test works with both 1.x and 2.x versions of PHPCS
- if "*.diff" file present then compares fixed version of file with expected one
- compares actual fixed error/warning count with expected ones
Merge pull request #32 from aik099/31-make-abstractsniffunittest-compatible-with-phpcs-2-x

Adapting "AbstractSniffUnitTest" to work with PHPCS 2.x