1.0.0.52

Removed pop-up previews for file attachments. This feature was causing
file attachments to become locked for some users, most likely due to a
Flash confliction.
Previously, the buttons to open file attachments were enabled regardless
of whether there was an attachment to load or not.  This would result in
loading 404 pages.  A HTTP Head request has been implemented to check
for the existence of the attached file as a web resource.  If it is not
present, the button for that attachment will be disabled.