Let setup_globals check for known globals

To avoid typos in calling setup_globals(), only allow
globals, which are already known to the system.
Plugins should have their own globals.

mediagoblin/tests/test_globals.py

@@ -14,6 +14,8 @@
 # You should have received a copy of the GNU Affero General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
+from nose.tools import assert_raises
+
 from mediagoblin import globals as mg_globals
 
 def test_setup_globals():
@@ -27,3 +29,8 @@ def test_setup_globals():
     assert mg_globals.database == 'my favorite database!'
     assert mg_globals.public_store == 'my favorite public_store!'
     assert mg_globals.queue_store == 'my favorite queue_store!'
+
+    assert_raises(
+        AssertionError,
+        mg_globals.setup_globals,
+        no_such_global_foo = "Dummy")