"Orderless" mining may require "Exact" to avoid a combinatorial explosion

[kliegr]

Issue #67 notes that orderless mining of a task with two atom patterns in the body may take very long if not combined with the "Exact" option which would prevent the addition of additional atoms to the body (if maximum rule length allows this).

It might be a good idea to explain this / warn the user in the help for the Orderless option.