Fix revlog.parseindex
parseindex could fail if read returns too little data in the right
moment (e.g. when there's still leftover data from the previous
iteration and read returns less than "s" bytes).
# repo.py - repository base classes for mercurial
#
# Copyright 2005 Matt Mackall <mpm@selenic.com>
#
# This software may be used and distributed according to the terms
# of the GNU General Public License, incorporated herein by reference.
class RepoError(Exception): pass