Redmine links can be used to link to documents, versions and attachments.

For now, attachments of the current object can be referenced only (if you're on an issue, it's possible reference attachments of this issue only).

git-svn-id: http://redmine.rubyforge.org/svn/trunk@1064 e93f8b46-1217-0410-a6f0-8f06a7374b81