topics: use a dict for successors of changesets produced by topic change This patch adds a dictionary to store the successors of changesets which got obsoleted when we change it's topic. This is an improvement in the fix for issue5441.

syntax: re
/figures/[^/]+\.png$
^html/
\.pyc$
~$
\.swp$
\.orig$
\.rej$
\.err$
^tests/easy_run.sh$
^build/
^dist/
^MANIFEST$
^docs/tutorials/.*\.rst$
\.ico$
tests/\.testtimes