Miscellaneous improvements to regression test framework, most notably

Miscellaneous improvements to regression test framework, most notably
changes regarding how events are processed. We now state what events
we are waiting for when calling run_loop. The central event dispatcher
monitors this list and decides when to pause the loop. Return value
from run_loop is the event name and whatever arguments were sent by
the event creator, if the event triggered no explicit handler, or
otherwise, the return value(s) from the event handler. If subsequent
events occur between a loop-pausing event and the time the loop
actually pauses, such events are queued and eligible candidates for
return value of the next call to run_loop. This way, events will not
be lost accidentally, which might happen in previous revisions.

git-svn-id: svn+ssh://projects.linpro.no/svn/varnish/trunk@1513 d4fa192b-c00b-0410-8231-f00ffab90ce4