Update llnet support.
Remove unused abort_http_parse variable.
Fix nil reference bug.
Return http parser to parser pool between requests.

This allows sharing of the parser object between http connections.
Fix request head timeout.  Fix max keepalive requests.
Only call parser:is_upgrade() once per http request.
Add buffer object.  Cleanup HTTP response generation.
Fix normalization of unknown http headers.
Improve speed of http headers dup.
Add ffi-based string.lower() function to replace NYI version on LuaJIT 2.0.x
Faster string.lower() replacement.
Catch Lua errors from event poller loop to allow gracefull shutdown.
Call error handler on connect() error.
Cleanup IO block/unblock logic.
Must check if the socket is closed in IO event callbacks.
Cleanup shutdown() method.
Make 'error' local.