tests/test-revlog-raw.py.out

help: document `$HG_NEW_OBSMARKERS` in pretxnclose hook

Differential Revision: https://phab.mercurial-scm.org/D10399

local test passed
addgroupcopy test passed
clone test passed
lowlevelcopy test passed
slicing test passed
issnapshot test passed
findsnapshot test passed