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
#
# Corrupt an hg repo with two pulls.
#

# create one repo with a long history
hg init source1
cd source1
touch foo
hg add foo
for i in 1 2 3 4 5 6 7 8 9 10; do
    echo $i >> foo
    hg ci -m $i
done
cd ..

# create a third repo to pull both other repos into it
hg init version2
hg -R version2 pull source1 &
sleep 1

hg clone --pull -U version2 corrupted
wait
hg -R corrupted verify
hg -R version2 verify