base href for passenger sub-URI deployment
The usefulness of this feature arises in the following scenario:
You deploy redmine using mod_rails a.k.a. Phusion Passenger's sub-URI method, but the sub-URI is a moving target. This is certainly possible. You deploy Redmine somewhere and then decide you want to change the URL.
Problem: But that breaks relative links in your wiki pages and elsewhere!
Solution: add a configuration setting called "sub-URI" to Administration->Settings->General, right after the setting named "Host name". If set, write this value as <base href='.......' /> inside <head> of app/views/layouts/base.rhtml
That way, when the administrator moves Redmine around under the web document root, he only needs to change the sub-URI setting and hyperlinks will work. This feature would increase Redmine's flexibility, make it more "portable", and make it easier to deploy using Passenger.