"default_workarounds" option should be set for SSL context member

in order to make HTTP client work properly with IIS server.
Without this option server will forcibly close connection at some point of time.
Thanks to Nikolay Peganov.
special isKeepAlive() method to check if connection can be cached

the keep-alive flag is varied for HTTP 1.0 and HTTP 1.1:
HTTP 1.0 uses "Connection: Keep-Alive" header
HTTP 1.1 uses keep-alive by default, until "Connection: close" is provided