namespace: use registrar to add template keyword
Prepares for switching to the new API.
templatekw: switch most of showlist template keywords to new API (
issue5779)
Non-trivial changes will follow.
py3: silence "bad escape" warning emitted by re.sub()
Since we pass user strings directly to re.sub(), we can't avoid this warning
without a BC.
debugcommands: add some strkwargs love to some **args calls
Differential Revision: https://phab.mercurial-scm.org/D2563