topic: centralize compatibility logic between hg versions into compat module This patch can delay loading obsutil and obsolete modules until they are actually used at "hg topics" or so, if demandimport of Mercurial is enabled.

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