add list of subclasses when using pinfo - etc

IPython/core/oinspect.py

@@ -639,6 +639,7 b' class Inspector(Colorable):'
 
             append_field(_mime, 'File', 'file')
             append_field(_mime, 'Type', 'type_name')
+            append_field(_mime, 'Subclasses', 'subclasses')
 
         else:
             # General Python objects
@@ -859,6 +860,9 b' class Inspector(Colorable):'
             if init_ds:
                 out['init_docstring'] = init_ds
 
+            names = [sub.__name__ for sub in obj.__subclasses__()]
+            all_names = ', '.join(names)
+            out['subclasses'] = all_names
         # and class docstring for instances:
         else:
             # reconstruct the function definition and print it: