Enable tracking of external bugs
I often have the problem that I track bugs in Redmine that are actually tracked or depend on bugs tracked in external bug trackers because they belong to external libraries or dependencies. It would be nice if Redmine could associate link bugs to bugs in external trackers (duplicates, dependencies) and track the upstream status by translating it to the Redmine equivalent. As this is very much specific to the software of the external tracker, this feature should be implemented as an API against which developers can develop tracker specific plugins like Bugzilla, Trac, etc.
An example of how this feature could look like can be seen on the launchpad bug tracker, eg. https://bugs.launchpad.net/ubuntu/+bug/1