http server: support persistent connections. only "hg serve" affected yet. http server running cgi script will not use persistent connections. support for fastcgi will help that. clients that support keepalive can use one tcp connection for all commands during clone and pull. this makes latency of binary search during pull much lower over wan. if server does not know content-length, it will force connection to close at end. right fix is to use chunked transfer-encoding but this is easier and does not hurt performance. only command that is affected is "changegroup" which is always last command during a pull.

pulling from ../a
searching for changes
abort: repository is unrelated
pulling from ../a
searching for changes
warning: repository is unrelated
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files (+1 heads)
(run 'hg heads' to see heads, 'hg merge' to merge)
changeset:   1:bdcee5d51fa6
tag:         tip
user:        a
date:        Mon Jan 12 13:46:40 1970 +0000
summary:     a

changeset:   0:f155ba1aa5ba
user:        b
date:        Mon Jan 12 13:46:40 1970 +0000
summary:     b