Defer to phpcs.xml/phpcs.xml.dist when present

[jhedstrom]

When a project's files grow beyond a certain point, the grunt validate task stops working since every single file to be validated is passed to the phpcs command.

The error is

Warning: spawn E2BIG Use --force to continue.

To avoid this, it seems like a good idea to defer to a phpcs.xml or phpcs.xml.dist file (phpcs itself will use these if no files are passed).