Swap the 'direction' of the bonds when closing rings

It doesn't really make any difference because the bonds
don't have a direction...a bond from atom 'a' to atom 'b'
is equivalent to a bond from atom 'b' to atom 'a'...but it
feels more natural for the ring closure bonds to go 'from'
the first atom with the ring closure label 'to' the second
atom with the label.

(It also makes it a bit easier when examining the results
and comparing with expected values, etc).