rework refactor _aspiringchildren by introducing _possibledestination
This allows us to reuse some of the logic for evolve from _aspiringchildren
for the new implementation of evolve --all.
The logic is also better as some previously selected changesets may not actually
evolve on the target, and some changesets that does not would not.
syntax: re
/figures/[^/]+\.png$
^docs/build/
^docs/html/
^html/
\.pyc$
~$
\.swp$
\.orig$
\.rej$
\.err$
^tests/easy_run.sh$
^build/
^MANIFEST$
^docs/tutorials/.*\.rst$
\.ico$