To add a directory without any of its contents/files to SVN you can do this:
(You need to be using SVN v1.5 or greater for this to work)
1svn add –depth=empty app/tmp
You can then SVN ignore the contents to prevent it being version controlled.
If you want to view changed/modified/added files from previous revisions with SVN you can do this:
12svn log -v -r 25
# This will show you the changes that were committed in v25
This section of the SVN book tells you how to roll back to previous versions, using the merge command on your working copy:
http://svnbook.red-bean.com/en/1.0/svn-book.html#svn-ch-4-sect-4.2