Deny direct variable type comparison

[zyluo]

According to PEP8,

- Object type comparisons should always use isinstance() instead
      of comparing types directly.

        Yes: if isinstance(obj, int):

        No: if type(obj) is type(1):

      When checking if an object is a string, keep in mind that it might be a
      unicode string too! In Python 2.3, str and unicode have a common base
      class, basestring, so you can do:

        if isinstance(obj, basestring):

People, including me, tend to import the types module and do something like "type(XXX) is types.IntType".

Comparing types directly should trigger an error.

[jendrikseipp]

+1

[florentx]

Done in trunk.
However I worry a little we have a risk to trigger false positives.