objhead lock, don't preallocate objects.

One unfortunate effect of this preallocation, only recently identified:

On systems with high number of worker threads and high hitrates, considerable
time could elapse between the preallocation of an object to a worker
thread and the use of that object.

This could make cache-misses use a much larger working set size than
really necessary.

I do not have access to any benchmarks that show a credible performance
difference, but reports are most welcome.




git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@3842 d4fa192b-c00b-0410-8231-f00ffab90ce4