http: respect HTTP/1.0 TE header

A HTTP/1.0 client does not support 'Transfer-Encoding: chunked' unless it
explicitly requests it by sending a 'TE: chunked' header.

Before this commit, node.js always disabled chunked encoding for HTTP/1.0
clients. Now it will scan for the TE header and turn on chunked encoding if
requested and applicable.

Fixes #940.