a change of key value.

Contrary to the previous comment in cache_expire.c, this process is
guaranteed to work because the shuffle will always terminate either
in the root position or in the bottom row.

Use this function when we adjust ttl on an object.



git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@5582 d4fa192b-c00b-0410-8231-f00ffab90ce4