invalid url might block project addition

Step 1: Trying to add a new project with the http url of pom's parent directory (i.e. the pom.xml in the end is missing), the directory list is retrieved resulting in a file
in the temp directory.
Step 2: Adding the full url including the pom.xml fails with the following error:

Could not download http://repository/svn/repository/trunk/test/pom.xml: /home/builduser/continuum-1.0.3/temp/continuum/svn/repository/trunk/test/pom.xml (Not a directory)

For this example, this can easily be fixed by manually removing the file "test" in the checkout directory.

The expected behavior would be that erroneously checked out files get cleaned up, so they might not block other projects. In the worst case, someone would add the
repository root (http://repository/svn/repository). So no one else might be able to add projects from the same directory without prior admin intervention.