Merge of r4920, r4939: ngx_write_chain_to_file() fixes. *) Core: added debug logging of writev() in ngx_write_chain_to_file(). *) Core: fixed ngx_write_chain_to_file() with IOV_MAX reached. Catched by dav_chunked.t on Solaris. In released versions this might potentially result in corruption of complex protocol responses if they were written to disk and there were more distinct buffers than IOV_MAX in a single write.