Proposed patch to fix #972

[Tollef Fog Heen]

]] Martin Blix Grydeland 

| After discussions with DocWilco and Tollef, we came to the conclusion that
| disabling streaming when meeting the conditions for 304 is a better
| solution.
| 
| Attached patch refactors the conditionals handling into a check and do
| function, and performs an extra check and disables if met when do_stream is
| true.

Maybe check sp->http->conds either in RES_Check_Conds or in
cnt_fetchbody too?

Apart from that, it looks reasonable to me.

-- 
Tollef Fog Heen
Varnish Software
t: +47 21 98 92 64