Reserve space for the objects entry in the index, when the object
is allocated.

Allow smaller than requested allocations for non-object allocations.

Attempt allocation from three segments, then give up.



git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@4270 d4fa192b-c00b-0410-8231-f00ffab90ce4