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.
abort: impossible time zone offset: 4444444
transaction abort!
rollback completed
abort: invalid date: '1\t15.1'
transaction abort!
rollback completed
abort: invalid date: 'foo bar'
transaction abort!
rollback completed
abort: invalid date: ' 1 4444'
transaction abort!
rollback completed
abort: date exceeds 32 bits: 111111111111
transaction abort!
rollback completed
abort: No such file or directory: .../test/bar