The original reasoning for having it private to cache_http.c was
to avoid pollution with event.h related structures but since that
pollution is happening other ways anyway, the cost is too high.

Include pthread.h, sys/time.h, and event.h from cache.h



git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@380 d4fa192b-c00b-0410-8231-f00ffab90ce4