always print FATAL and ERROR logmessages to STDERR

always print FATAL and ERROR logmessages to STDERR

This adds a print to $stderr for log messages with the
level ERROR or FATAL. I did this because in the past errors
connecting to the server weren't immediately obvious but
rather hidden in the logfile. I think it should be right
in-your-face when the connection doesn't work.

It would probaply be better to extend Logger to print
to STDERR but this apparently requires monkeypatching ruby's
Logger. Anyhow I think my solution works for now.