chg: downgrade "failed to read channel" from abortmsg to debugmsg If the server has an uncaught exception, it will exit without being able to write the channel information. In this case, the client is likely to complain about "failed to read channel", which looks inconsistent with original hg. This patch silences the error message and makes uncaught exception behavior more like original hg. It will help chg to pass test-fileset.t.