In that case, provide a value for $wgServer; set *that* to the hostname.
I added one line to LocalSettings.php: $wgServer = "hostname";
Then after I restart apache & mysql and edit a page, when I save the edit I get sent to URL:
http://hostname/wiki/hostnamehostname/wiki/index.php/name_of_edited_page
When I manually edit the URL to be http://hostname/wiki/index.php/name_of_edited_page, it shows the edit to have been saved. So this is not a disaster, just kinda embarrassing.
Thanks for the input!
Dave