_repr_html_ exception reporting corner case when using type(foo)

[ghost]

@michaelaye reported this in pandas-dev/pandas#6225,
but it seems to be an ipython issues, resulting from the recent #4745.

In [11]: class Foo(object):
    ...:     def _repr_html_(self):
    ...:         return "Me"
    ...: x=Foo()
In [12]: type(x)
/home/user1/src/ipython/IPython/core/formatters.py:199: FormatterWarning: 
Exception in text/html formatter: unbound method _repr_html_() must 
be called with Foo instance as first argument (got nothing instead)
  FormatterWarning,

[takluyver]

Looks like we check for the existence of a _repr_foo_ attribute, but not whether it can be called with no arguments.