Fix error in test suite startup with dotted import names.

Detected first on ubuntu 12.04, but the bug is generic, we just hadn't
seen it before.  Will push straight to master as this will begin
causing problems as more people upgrade.

IPython/utils/importstring.py

@@ -38,6 +38,10 b' def import_item(name):'
 
     if package:
         module = __import__(package,fromlist=[obj])
-        return module.__dict__[obj]
+        try:
+            pak = module.__dict__[obj]
+        except KeyError:
+            raise ImportError('No module named %s' % obj)
+        return pak
     else:
         return __import__(obj)