Duplicate Link Validation

[cvestre]

When a user creates a new link and the URL has already been registered under a different short name, alert the user and list the existing short name(s).

Should multiple short names be allowed to point to the same link?

[mbland]

There should at least be a warning, so that the user has the option of using the existing link, contacting the original link owner, or going ahead with creating the new one.