webrick: avoid unnecessary IO#sync= call

	Sockets and pipes are always created with FMODE_SYNC flag
	already set (otherwise many things would be broken).

	* lib/webrick/server.rb (accept_client): remove unnecessary
	  IO#sync= call

	webrick: do not hang acceptor on slow TLS connections

	OpenSSL::SSL::SSLSocket#accept may block indefinitely on clients
	which negotiate the TCP connection, but fail (or are slow) to
	negotiate the subsequent TLS handshake.  This prevents the
	multi-threaded WEBrick server from accepting other connections.

	Since the TLS handshake (via OpenSSL::SSL::SSLSocket#accept)
	consists of normal read/write traffic over TCP, handle it in the
	per-client thread, instead.

	Furthermore, using non-blocking accept() is useful for non-TLS
	sockets anyways because spurious wakeups are possible from
	select(2).

	* lib/webrick/server.rb (accept_client): use TCPServer#accept_nonblock
	  and remove OpenSSL::SSL::SSLSocket#accept call
	* lib/webrick/server.rb (start_thread): call OpenSSL::SSL::SSLSocket#accept
	* test/webrick/test_ssl_server.rb (test_slow_connect): new test
	  [ruby-core:83221] [Bug #14005]

	webrick: fix up r60172

	By making the socket non-blocking in r60172, TLS/SSL negotiation
	via the SSL_accept function must handle non-blocking sockets
	properly and retry on SSL_ERROR_WANT_READ/SSL_ERROR_WANT_WRITE.
	OpenSSL::SSL::SSLSocket#accept cannot do that properly with a
	non-blocking socket, so it must use non-blocking logic of
	OpenSSL::SSL::SSLSocket#accept_nonblock.

	Thanks to MSP-Greg (Greg L) for finding this.

	* lib/webrick/server.rb (start_thread): use SSL_accept properly
	  with non-blocking socket.
	  [Bug #14013] [Bug #14005]

	webrick: fix up r60172 and revert r60189

	Thanks to MSP-Greg (Greg L) for helping with this.

	* lib/webrick/server.rb (start_thread): ignore ECONNRESET, ECONNABORTED,
	  EPROTO, and EINVAL on TLS negotiation errors the same way they
	  were ignored before r60172 in the accept_client method of the
	  main acceptor thread.
	  [Bug #14013] [Bug #14005]

	webrick: fix up r60172 and r60208

	Thanks to MSP-Greg (Greg L) for helping with this.

	* lib/webrick/server.rb (start_thread): fix non-local return
	  introduced in r60208

	webrick: fix up r60172 and r60210

	Thanks to MSP-Greg (Greg L) for helping with this.

	* lib/webrick/server.rb (start_thread): properly fix non-local return
	  introduced in r60208 and r60210

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_4@61239 b2dd03c8-39d4-4d8f-98ff-823fe69b080e