Initial dumb version of topics.

serveronly: deduplicate code with the main evolve extension Now that 'serveonly' is a sub module of evolve. We can access its content in evolve. As a result we stop duplicating code all common parts are defined in the 'serveronly' module and imported by evolve when needed.

serveronly: clean up imports remove unused one and arrange them

compat: just use '_callcompressable' That API is available in all version we supports.

compat: drop bookmark compatibility layer All the version we now supports have the 'new' API.

compat: drop compat for older wireproto implementation We only support Mercurial version with these attributes.

compat: always use the strip revset from core We only support versions that defines it.

compat: drop support for ancestral pushop object Pushoperation object have a 'cgresult' attribute in all the versions we support.

compat: drop compatibility layer around update We now support only versions with the new API.

compat: drop compatibility layer for 'tryimportone' Return is now homogeneous for all the version we support.

compat: drop superfluous summary output All versions we support issues this output.

compat: drop compatibility layer around memctx The version we support all have the same API now.

compat: drop handling of ancestral 'helploader' caller We only support recent only version on Mercurial now.

compat: drop hack around a 'graft' signature change We only support recent only version of Mercurial now.

evolve: proactively detect bad version early The extensions have been providing such error to the user for some time. So we keep this explicit check (instead of some later errors). The check is update to match out new version constraint.