Make it possible to avoid -fstack-protector on OmniOS

Submitted by:	fgs
Fix paste error on my diff so --disable-stack-protector really works
Inject another BOS_STATE, to tell if we have committed to action
in vcl_backend_response{}
Gah!  spell "committed" right.
Fix double-logging of synth 503 beresp.
Turn the confusion of busyobj flags into a #include table.
Get a new bereq XID  if we retry a fetch
VFP_Error() is only for use after vcl_backend_response{} has run.
Handle the case where too many retries are attempted, by returning
a 503 reply.

Fixes #1401