This fixes a confusing issue where doing 'merchant.setRecipes(merchant.getRecipes());' would clear the merchants recipes, as the implementation of getRecipes is guavas Lists.transform wrapped in Collections.unmodifiableList, and the implementation of setRecipes clears the backing list before adding the elements of the provided list to the backing list.
The javadoc for the getRecipes method says 'an immutable list of trades', so this patch makes the javadoc correct.
