Show real class name

[erikbgithub]

When someone is extending ConfigObj the String should show the actual class name as well.

e.g.:

>>> class MyConfigObj(ConfigObj):
...     pass
>>> o=MyConfigObj()
>>> o
MyConfigObj({})

instead of

>>> o
ConfigObj({})

[coveralls]

Coverage remained the same when pulling d7ddf28 on erikb85:master into d00c202 on DiffSK:master.

[EliAndrewC]

This seems good to me - thanks a bunch for the pull request and for including such a handy code snippet in the description.