chgserver: invalidate the server if extensions fail to load
Previously, if extensions fail to load, chg server will just keep working
without those extensions. It will print a warning message but only if a new
server starts.
This patch invalidates the server if any extension failed to load, but still
serve the client (hopefully just) once. It will help chg pass some test cases
of test-bad-extension.t.
(binary:application/octet-stream)