[imp] secure connection only

[Lars Hecking]

> Well, checking the apache docs, and trying lots of things.... I found that 
> this was the best solution:
> 
> RewriteEngine On
> RewriteRule /horde/imp/.* https://math.unl.edu.ar/horde/imp/ [R]
> 
> Ofcourse, I have the rewrite module compiled and loaded. I'm open to 
> opinions, cuase maybe I did something that is not very pleasent for the 
> apache.

 To make this more efficient:
 - use the rewrite rule only in the horde directory, not in server context
 - rewrite only http connections, not https connections

 <Directory /usr/local/htdocs/horde>
      # you need FollowSymLinks if you use the rewrite engine
      # in directory context - see mod_rewrite docs
      Options Indexes FollowSymLinks
 [other stuff]
      RewriteEngine On
      RewriteCond %{HTTPS}       !=on
      RewriteRule ^(.*)$         https://%{SERVER_NAME}/webmail/ [L]
 </Directory>

 This specific example assumes that /webmail is aliased to /horde/imp.