File attachments plugin: If directory is not writeable or otherwise invalid,...

File attachments plugin: If directory is not writeable or otherwise invalid, the admin will see a warning in the "notifcations" area

git-svn-id: https://svn.viathinksoft.com/svn/oidplus/trunk@1180 02e4d621-2042-4998-a0bc-9ccd24201011