Fixes project jumping behaviour.

Restores original behaviour of project selection - jumping to the part
of the target project that corresponds to where the user is right now in
the current project.
Merge pull request #18 from finnlabs/fix/project-jump-behaviour

Fixes project jumping behaviour.
sets rails to 2.3.16
fixes issue diff link when having a relative_url_root defined

Because relative_url_root gets applied along with Setting.host_name having the same root when constructing the link the root is included two times in the resulting link. This is accounted for with this fix. There is a better method of doing so but this would require OpenProject to use rails 3.2 and we are not there yet.
Merge branch 'fix/issue_description_diff_relative_url_root' of github.com:opf/openproject into fix/issue_description_diff_relative_url_root