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.
#!/bin/sh
hg init test
cd test
echo foo > foo
hg add foo
hg commit -d '0 0' -m commit-1
echo foo >> foo
hg commit -d '1 4444444' -m commit-3
hg commit -d '1 15.1' -m commit-4
hg commit -d 'foo bar' -m commit-5
hg commit -d ' 1 4444' -m commit-6
hg commit -d '111111111111 0' -m commit-7
echo bar > bar
hg add bar
rm bar
hg commit -d "1000000 0" -m commit-8 2>&1 | sed -e "s:/.*\(/test/.*\):...\1:"
exit 0