add support for streaming clone. existing clone code uses pull to get changes from remote repo. is very slow, uses lots of memory and cpu. new clone code has server write file data straight to client, client writes file data straight to disk. memory and cpu used are very low, clone is much faster over lan. new client can still clone with pull, can still clone from older servers. new server can still serve older clients.

#!/bin/sh

set -e

mkdir test
cd test
echo foo>foo
hg init
hg addremove
hg commit -m "1"
hg verify

hg clone . ../branch
cd ../branch
hg co
echo bar>>foo
hg commit -m "2"

cd ../test
hg pull ../branch
hg verify
hg co
cat foo
hg manifest