evolve: add a test reflecting wrong behaviour of content-div resolution This patch shows that currently the case when stack of divergent csets have different parents is not handled correctly. For a stack of csets which has different parent, right behaviour is to relocate every node before performing merge but present implementation only relocate first cset in the stack and skip relocation for the rest of csets, this is not what we expect it to do. Next patch will be about fixing this issue.

compat: add support for new arg name in memfilectx.__init__ This makes us compatible with 550a172a603b (memctx: rename constructor argument "copied" to "copysource" (API), 2019-03-19).

evolve: preserve compatibility for hg < 4.8 versions This patch make sure evolve don't break if user using a version of hg before this 7694b685bb10 patch on hg-committed.

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.