 
mod_userdir: implement the UserDir command.
Broken away from the Alias stuff for a couple of good and not-so-good
reasons:

1) It shows a real minimal working example of how to do something like
   this.
2) I know people who are actually interested in changing thisparticular*
   aspect of server functionality without changing the rest of it.  That's
   what this whole modular arrangement is supposed to be good at...

Modified by Alexei Kosut to support the following constructs
(server running at www.foo.com, request for /~bar/one/two.html)

UserDir public_html      -> ~bar/public_html/one/two.html
UserDir /usr/web         -> /usr/web/bar/one/two.html
UserDir /home/ /www     -> /home/bar/www/one/two.html
 NOTE: theses ^ ^ space only added allow it to work in a comment, ignore
UserDir http://x/users   -> (302) http://x/users/bar/one/two.html
UserDir http://x/ /y     -> (302) http://x/bar/y/one/two.html
 NOTE: here also ^ ^

In addition, you can use multiple entries, to specify alternate
user directories (a la Directory Index). For example:

UserDir public_html /usr/web http://www.xyz.com/users

 
