errors: raise RemoteError in some places in exchange.py
This is part of https://www.mercurial-scm.org/wiki/ErrorCategoriesPlan
Differential Revision: https://phab.mercurial-scm.org/D10467
# The 9diff extdiff command generates diff(1) compatible output
# suitable for use with the plumber(4).
[extensions]
extdiff =
[extdiff]
9diff = /bin/mercurial/9diff -cm $parent $child $root