Case Activity attachments sometimes do not display the paperclip icon

See https://issues.civicrm.org/jira/browse/CRM-10712 for the original implementation.

A client recently ran into the problem where the paperclip icon for attachments wasn't showing up for some Case Activities.

For some reason, $dao->attachment_ids sometimes returns duplicates of a file ID, which caused this to think there were multiple file attachments, and thus did not output the paperclip icon.

Also noted that there is no behaviour for multiple attachments. Not even a counter as an indicator.

We've written a small change for Case.php to do the following:

1. Ensure the array of $attachmentIDs only includes unique IDs.
2. For multiple attachments (>1), output the paperclip icon with a counter to indicate number of attachments on the Activity.

PR on the way.