evolve: warn user if cset desc is being lost
In public divergence when merging results in same as public cset,
we only create markers to solve the divergence i.e. [(public, (other,))]
In this case if other cset had a desc which was different from public
that will be lost.
So this print out a warning message to user that desc of non-public
cset is being lost.
Changes in test files reflect the added behaviour.