issue186 discusses the same problem more generally, so closing this issue

As long as return code semantics are clearly stated like grep it should be ok to
go with individual exit codes. I guess it depends on what level of detail you
are looking for. To me as long as hg pull worked, no matter it got new files or
there were none, it is success. To you if nothing was pulled it is 1, if
something was pulled 2, if something broke it is 3 etc.

Think of grep: It returns 1 if the pattern was not found and 2 if the file was
not found (at least for GNU grep)

This goes against the traditional way of checking exit codes. An operation
should only return a non-zero exit status if some error occured. Ignoring the
return value requires using another operation to see what happened to the pull
i.e. operation failed, succeeded and no changes were pulled or succeeded and
some changes were pulled.

This is used for things like:  hg pull && do_something_if_new_changesets
You can easily ignore the exit code with:  hg pull || true