Explain ERC 5.5 regressions in new version 5.5.0.29.1

Explain ERC 5.5 regressions in new version 5.5.0.29.1

* doc/misc/erc.texi: Bump version to 5.5.0.29.1.
* etc/ERC-NEWS: Don't hype bugged option `erc-reconnect-display'.
* lisp/erc/erc-dcc.el (erc-dcc-do-GET-command): Add comment explaining
parsing bug in ERC 5.5 (bug#62444).
* lisp/erc/erc-networks.el (erc-networks-on-MOTD-end): Mention known
/MOTD bug in error notice so people don't waste energy reporting
it (bug#62151).
* lisp/erc/erc.el: Change Version header to 5.5.0.29.1.  Don't bother
updating the `customize-package-emacs-version-alist' entry
because no option defaults are affected.
(erc-version): Change version to 5.5.0.29.1.
(erc-reconnect-display, erc-query-on-unjoined-chan-privmsg): Add
warning to doc strings and `custom-set' functions.  It's believed that
these bugs degrade the user experience significantly enough to warrant
such mentions (bug#62833).
(erc-query): Fix erroneous redirect string in deprecation spec.
Do not merge to master.