SPDY: refactored ngx_http_spdy_state_headers().
SPDY: refactored ngx_http_spdy_state_headers().

This change is similar to d2ac5cf4056d.  Special flag of completeness looks
surplus when there is also a counter of frame bytes left.

firebase/nginx,hy0kl/nginx,firebase/nginx,hy0kl/nginx,firebase/nginx,firebase/nginx,hy0kl/nginx