HTTP/2: fixed splitting of response headers on CONTINUATION frames.
HTTP/2: fixed splitting of response headers on CONTINUATION frames.

Previous code has been based on assumption that the header block can only be
splitted at the borders of individual headers.  That wasn't the case and might
result in emitting frames bigger than the frame size limit.

The current approach is to split header blocks by the frame size limit.

hy0kl/nginx,hy0kl/nginx,hy0kl/nginx