Handle synchronous errors when connecting asynchronously

In jabber-network-connect-async, the call to make-network-process can
fail in certain cases without creating a connection and without
calling our sentinel function, in particular if DNS resolution fails,
and that error case was not updated for the new error reporting
solution.  This should now work properly.
Fix argument name

s/js/jc/.  This code happened to work anyway because of dynamic scoping.
Trim trailing newline from sentinel status messages
Fix handling of stream errors

This was overlooked when introducing namespace handling: the namespace
prefix is no longer part of the element name, and the namespace can be
looked up through a fictitious xmlns attribute.