I18N fixes and (hopefully) protocol fixes

* Correct some grammar in German translation (extraneous "vor").

* Try to fix desyncs when an older channel bursts in after initial join.

* Languages must be subdirectories that do not start with '.', so
  check that before applying them as a language.  Since we already
  have the language list at helpfile_finalize() time, use it instead
  of walking the "languages" directory again.

* Ignore 467 response from uplink.
git-archimport-id: srvx@srvx.net--2004-srvx/srvx--devo--1.3--patch-42