Apparently this a known thing at my webhost that when the WordPress administrator changes the base url settings from, say http://foo.com to http://bar.com, WordPress drops an .htaccess file in the wrong place.  Instead of putting it in /var/www/html/wordpress/.htaccess, it puts it in /.htaccess causing all of Apache’s served pages to return a 500 server error.

Does anyone else have that problem?  It certainly raised my blood pressure when everything suddenly went down.  Good thing WestHost has great tech support.