Improve output of error messages

[odrotbohm]

Constraints can return data that will be included in the output of error messages on the command line. Currently all variable values will be printed comma separated which makes them hard to read, especially for long values (e.g. fully qualified class names).

It would be cool if they could be separated by a new line instead:

someVariable=com.acme.FooBar
someOtherVariable=…