in critbit to avoid a malloc in the locked path.

Move the waitinglist to its own structure in preparation for Big
Things Afoot which will give it more work to do.  This saves a
pointer in objhead on average, always a good thing.

Have the worker thread preallocate a waitinglist structure.



git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@5615 d4fa192b-c00b-0410-8231-f00ffab90ce4