add merge command. means same thing as "update -m". repo.addchangegroup method now returns number of heads modified and added, so command line can tell whether update or merge needed. this makes tiny change to ssh wire protocol, but change is backwards compatible. pull command now returns 0 if no changes to pull.

requesting all changes
abort: error: Connection refused
255
copy: No such file or directory
requesting all changes
abort: HTTP Error 404: File not found
255