bugfix: ngx.req.raw_header() could lead to buffer overflow and the "userdata length overflow" error due to misuse of r->header_end while modules like ngx_fastcgi and ngx_proxy can change r->header_end to point to buffers of their own. thanks sadmedved for the report.
bugfix: ngx.req.raw_header() would return garbled data when LF instead of CRLF is used as the line terminator in the original header.