bugfix for #79411 Connect with invalid password exits

[pmorch]

This is a fix for Bug #79411 for Net--RabbitMQ: Connect with invalid password exits

The problem was that write was called on closed sockets. That caused SIGPIPE signals that weren't handled.

It is fixed by introducing write_ignore_pipe_signal() that sets up a short-lived signal handler SIGPIPE that simply ignores the signal while write() is called.

write_ignore_pipe_signal() is now called everywhere that write() used to be called directly.