initial version of monotone source for convert extension

notify: print diffstat even if maxline == 0

Make clear that for a changegroup '-r' pulls "up to" a revision If some better wording is found, it can be changed later.

two fixes for the pager stuff - open pipe in binary mode - don't start a pager if stdout is not a tty (this prevents test-ssh from hanging if you set ui.usepager=True in run-tests.py)