When used:
* outside of a project: searches projects
* inside a project: searches issues, changesets, news, documents and wiki pages of the current project

If an issue number is given, user is redirected to the corresponding issue.

git-svn-id: http://redmine.rubyforge.org/svn/trunk@489 e93f8b46-1217-0410-a6f0-8f06a7374b81