Python3.5: Make sure our "isinstance" replacement has a signature too.
Python3.5: Make sure our "isinstance" replacement has a signature too.

* Actually it just takes "__doc__" to have that, copy it over from the
  original one.

* Adding "__doc__" applies to all Python versions, but is probably very
  unimportant there.

kayhayen/Nuitka,kayhayen/Nuitka,kayhayen/Nuitka,kayhayen/Nuitka