Link URI re: issue 486

The proposed changes address the silent failing of adding a link to an unrecognized URI. They allow the user to correct any potential mistakes made to the initial address through a prompt dialogue. 
Haven't tried and it's a bit of a hack, but you could add the following to `attachLink.xul` (towards the top under the other script elements):
```
<script type="application/x-javascript">
  Zotero_AttachLink.linkToFileMessage = "&zotero.items.menu.attach.fileLink;"
</script>
```
It's a bit risky, since an internal double quote would break this, but I looked through all translations and there is no double quote for this string. The question is whether Dan feels comfortable with this in the long run.

Source: http://forums.mozillazine.org/viewtopic.php?f=19&t=1071895