fastcgi: Don't set CONTENT_LENGTH unless needed.
fastcgi: Add inet_ntop include in fcgi_env.
fastcgi: Fixup of trace and debug messages.

Fix format warning in printf.

Check return from event_add.

Check return of fcgi_fd state change.

Remove some redundant trace messages.
fastcgi: Let default for MaxConnections be 1.
fastcgi: Auto-generate LocationName if none given.
fastcgi: Indicate which variables are required in config.
fastcgi: Update minimal libfcgi config example.
fastcgi: Fix conditional close of fastcgi connection.
fastcgi: Compatibility with SSL transport.

Use mk_api->socket* on client socket and unistd functions on fastcgi
socket.
fastcgi: Set HTTPS in cgi environment.
fastcgi: Set version.