Better old-style class support

[ngaya-ll]

Treat old-style classes like types when validating. Prior to this patch, old-style classes in Python 2 would be treated like callables, leading to unexpected behavior.

>>> from plistlib import Data  # old-style class from standard library
>>> from voluptuous import Schema
>>> schema = Schema(Data)
>>> schema(Data('abc'))
Data(Data('abc'))
>>> schema('abc')
Data('abc')

With this patch, old-style classes are treated the same as types. This leads to better consistency between new-style and old-style classes.

>>> from plistlib import Data  # old-style class from standard library
>>> from voluptuous import Schema
>>> schema = Schema(Data)
>>> schema(Data('abc'))
Data('abc')
>>> schema('abc')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "voluptuous/schema_builder.py", line 225, in __call__
    raise er.MultipleInvalid([e])
voluptuous.error.MultipleInvalid: expected Data

[coveralls]

Coverage remained the same at 95.652% when pulling f47615a on ngaya-ll:master into 2a690a8 on alecthomas:master.

[coveralls]

Coverage remained the same at 95.652% when pulling a404944 on ngaya-ll:master into 2a690a8 on alecthomas:master.

[tusharmakkar08]

This PR looks fine to me. Please update CHANGELOG.md mentioning the changes.

[coveralls]

Coverage remained the same at 95.652% when pulling 25da46e on ngaya-ll:master into 2a690a8 on alecthomas:master.