Handle external issues in IssueReferenceFilter
Rendering issue references such as `#1` was broken for projects using an external issues tracker.
See gitlab-org/gitlab-ce#19036
See merge request !4988
(cherry picked from commit 6e82c0e0)
Handle external issues in IssueReferenceFilter
Rendering issue references such as `#1` was broken for projects using an external issues tracker.
See gitlab-org/gitlab-ce#19036
See merge request !4988
(cherry picked from commit 6e82c0e0)
