make data URLs ignore base URLs


git-svn-id: svn+ssh://svn.gna.org/svn/gnustep/libs/base/trunk@36150 72102866-910b-0410-8b05-ffd578937521
a few more tests


git-svn-id: svn+ssh://svn.gna.org/svn/gnustep/libs/base/trunk@36151 72102866-910b-0410-8b05-ffd578937521