implement notifyClosedInput0 and notifyClosedOutput0; comment shutdownOutput0
Merge branch 'master' into socket-natives
clarify comment; remove warning; add semi-colon
ensure buffered output gets written before returning from notifyClosedOutput
replace impls with conditional warnings for now
Merge pull request #197 from mykmelez/socket-natives

implement Protocol's shutdownOutput0, notifyClosedInput0, and notifyClosedOutput0 natives