TS-1086: Avoid returning 304 to an unconditional request.
Diagnosis and patch by Mohamad Khateeb.
TS-2191 we should not simply reschdule the http_sm if the sm_list`s mutex
is not acquired, because the client_vc`s timeout events maybe triggered.
The race may lead http_sm received a event after it is deleted.
Sub task (TS-2192)