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.

--- a/tests/test-pull	Thu Jul 13 09:50:51 2006 -0700
+++ b/tests/test-pull	Fri Jul 14 11:17:22 2006 -0700
@@ -11,7 +11,7 @@
 cat hg.pid >> $DAEMON_PIDS
 cd ..
 
-http_proxy= hg clone http://localhost:20059/ copy
+http_proxy= hg clone --pull http://localhost:20059/ copy
 cd copy
 hg verify
 hg co