topics: add a config to reject draft changeset without topic on a server This patch adds a new config option experimental.topic-mode.server which if sets to True, the server won't accept any draft changeset without topic on it. In case both `experimental.topic-mode.server` and `experimental.topic.publish-bare-branch` are set to True, the enforce-topic one is respected. Tests are added for it. The CHANGELOG file is also updated mentioning about the config option.

#require test-repo pyflakes

Copied from Mercurial core (60ee2593a270)

  $ cd "`dirname "$TESTDIR"`"

run pyflakes on all tracked files ending in .py or without a file ending
(skipping binary file random-seed)

  $ hg locate 'set:(**.py or grep("^#!.*python")) - removed()' 2>/dev/null \
  > | xargs pyflakes 2>/dev/null