A bit of cleanup while I ponder ticket 412:

make VBE_free_bereq() and HSH_Deref() null their argument pointer.

Add HSH_Drop() for deorbiting unwanted busy objects.



git-svn-id: http://www.varnish-cache.org/svn/branches/2.0@3658 d4fa192b-c00b-0410-8231-f00ffab90ce4