attachment list includes new attachments in holding area

Note that it's possible for an attachment in the holding area to be older
than an attachemnt in the wiki with the same name. I intentionally
show the one in the holding area in this (unlikely) case, since saving the
page will overwrite the wiki's file with the held attachment. It does not
seem worth the bother of doing something more intelligent, since in this
case two people have basically conflicted with one-another.. and both
attachment contents will be stored in revision control in case it needs to
be sorted out.

I had to remove the hyperlink for attachments in the holding area, since
they're not yet live on the web. This could be annoying/confusing. Added
a moseover notice instead.