This should address the issue raised by Michael J. Ryan in issue #4.
The command in question ("GROUP") would attempt to open the message
base associated with the specified newsgroup name without closing
the currently open/selected message base (if there was one). This would
result in multiple simultaneously open message bases and could result
in an exhaustion of open file descriptors leading to a failure to open
any additional files (includign message bases) and thus a subsequent
"GROUP" command would fail with the wrong "!no such group" error.