tests: add tests of content+parent change creating phase-divergence This patch adds tests which shows handling of phase divergence cases by `hg evolve` command which involved content+parent change. The conflicts case is not handled and will be fixed in upcoming patches.

tests: show first line of commit message in test-evolve-phase-divergence.t This patch adds 'firstline' filter to description in the log template.

evolve: make sure bookmarks are moved after phase-divergence resolution This patch adds logic to move bookmarks from the rebased node to the phase-divergence resolved node.

evolve: use the new rebased changeset to resolve phase-divergence When there is a parent change in phase-divergence, `hg evolve` first rebases the diveregent changeset on parent of public changeset and then continue the resolution of phase-divergence *but* we used to continue with the old divergent changeset rather than the new rebased one. This patch makes sure we use the new rebased changeset to proceed with the resolution. Tests changes shows that it fixes things which were broken earlier.

evolvecmd: add a detailed comment and some newlines This patch adds a detailed comment on a chunk and some newlines to make things look better and more understandable for upcoming patches.

tests: add one more test case about handling of phase-divergence by evolve This patch adds a test case when phasedivergence is caused by rebase command and there is parent change involved. As the tests show, we are not handling things correctly here. Upcoming patches will fix that. Fixing things in later patches showed there was a wrong case in one another test which will be fixed by later patches, so let's add description on why that test is wrong in this patch.