Put an upper limit on how many sessions we will allocate before we
just drop new connections summarily.

The parameter is session_max, default is 100k and the stats variable
client_drop counts how many sessions were dropped.

This is mostly an anti-DoS measure and your feedback and experience
with it is most welcome.


git-svn-id: http://www.varnish-cache.org/svn/branches/2.0@4260 d4fa192b-c00b-0410-8231-f00ffab90ce4