cmdserver: write early exception to 'e' channel in 'unix' mode In 'unix' mode, the server is typically detached from the console. Therefore a client couldn't see the exception that occurred while instantiating the server object. This patch tries to catch the early error and send it to 'e' channel even if the server isn't instantiated yet. This means the error may be sent before the initial hello message. So it's up to the client implementation whether to handle the early error message or error out as protocol violation. The error handling code is also copied to chgserver.py. I'll factor out them later if we manage to get chg passes the test suite.