http client: support persistent connections. uses keepalive module from urlgrabber package. tested against "hg serve", cgi server, and through http proxy. used ethereal to verify that only one tcp connection used during entire "hg pull" sequence. if server supports keepalive, this makes latency of "hg pull" much lower.

# 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