Override makeTest to correctly support path/to/test.py:test_function syntax.

If we don't explicitly override this, the checker used isn't IPython-aware and
we don't get full support for things like #random markers, when using the
syntax::

iptest tests/test_magic.py:doctest_clear_array

IPython/testing/plugin/ipdoctest.py

@@ -806,6 +806,23 b' class IPythonDoctest(ExtensionDoctest):'
     name = 'ipdoctest'   # call nosetests with --with-ipdoctest
     enabled = True
     
+    def makeTest(self, obj, parent):
+        """Look for doctests in the given object, which will be a
+        function, method or class.
+        """
+        # always use whitespace and ellipsis options
+        optionflags = doctest.NORMALIZE_WHITESPACE | doctest.ELLIPSIS
+
+        doctests = self.finder.find(obj, module=getmodule(parent))
+        if doctests:
+            for test in doctests:
+                if len(test.examples) == 0:
+                    continue
+
+                yield DocTestCase(test, obj=obj,
+                                  optionflags=optionflags,
+                                  checker=self.checker)
+
     def configure(self, options, config):
 
         Plugin.configure(self, options, config)