Revert "only enable colors when output to a terminal (not to a file)"

This reverts commit 591efd8fad55a526f021cad9c6cbcd9081df8969.
Rework 591efd8fad55a526f021cad9c6cbcd9081df8969
Merge branch '4.4'
Merge branch 'master' of git://github.com/sebastianbergmann/phpunit