new (bugfix) version of Kwiki::Attachments

Kwiki::Attachments 0.15 works with Kwiki 0.38.

I have also relaxed the filename filter a little to allow '-', '&' and 
'+' along with 0-9A-Za-z.  I plan to change the filename filter to allow 
unicode characters in the next release.

I welcome complaints/suggestions.

-sue