merge with stable throug 3.6 branch

merge with stable through 3.7 branch dropped the topic test and updated output with some minor difference Hg: Enter commit message. Lines beginning with 'HG:' are removed.

mercurial-3.7: revert output change No feature regression but various output change

merge default into stable Mercurial 3.8 have been release, let's get ready for a 5.4.0 release.

test: rename TOPICROOT to HGTEST_TOPICROOT Mercurial is about to introduce whitelisting of environment variable, we comply to the planned prefix in advance in a hope to stay compatible in the future.

test: update topic test output for order change As in topic d8f1e432b16a the tipmost changeset is now displayed first. We adapt the test output to reflect it.

test: update topic test output for indexing change Changeset 61f36480740f in topic updated the indexing scheme, we update the test to take this into account.

test: adapt topic test The 'created new head' bug was fixed in bdc5bb223b50, we adapt the test with the fixed output.

test: improve skipped message for topic The skipped message should point people to a way to solve the situation.

prune: suggest --biject in error "hint" When use specify multiple changesets to prune and as successors, we should point them to the right options to confirm there intend.

metaedit: check for public changeset before instability Public changeset will stay public even if the selection is adjusted, this is a more definitive condition that is worth warning about first.

fold: move sanity check after locking Checking for operation validaty without the locks open us to race condition.