Use file name of attachment instead of the unusable default name when adding a file in Documents.

1. Go to Groups, Documents and attach a file, for example I uploaded forum.png. http://next.dev.curriki.org/xwiki/bin/view/Group_CurrikiLeadersGroup/Documentation#
2. Go to Groups, Home, Recent Group Activity

Bug:
The activity looks like this: Feb-12-2008 - 02:52 PM Wiki document updated - "zVTZO8VJR7oa1Y21" by Todd Sherman
When it should look like this: Feb-12-2008 - 02:52 PM Wiki document updated - "<filename>" by Todd Sherman

Feel free to manipulate the File Name provided by the user in any way to avoid problems. For example, if you need to get rid of spaces do so. I will leave this up to you.