raise_from does not behave exactly like raise from

Here's a bit of sample code from [https://www.python.org/dev/peps/pep-3134/](PEP 3134):

class DatabaseError(Exception):
    pass

class FileDatabase(object):
    def __init__(self, filename):
        try:
            self.file = open(filename)
        except IOError as exc:
            raise DatabaseError('failed to open') from exc

fd = FileDatabase('dne')

This, of course, does not work on Python 2. Using Python 3 I get the following output:

Traceback (most recent call last):
  File "pepex2.py", line 7, in __init__
    self.file = open(filename)
FileNotFoundError: [Errno 2] No such file or directory: 'dne'

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "pepex2.py", line 11, in <module>
    fd = FileDatabase('dne')
  File "pepex2.py", line 9, in __init__
    raise DatabaseError('failed to open') from exc
__main__.DatabaseError: failed to open

When using raise_from for Python2 compatibility

from future.utils import raise_from
# [...]
            raise_from(DatabaseError('failed to open'), exc)

this output (still with Python3) changes to:

FileNotFoundError: [Errno 2] No such file or directory

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "pepex2.py", line 13, in <module>
    fd = FileDatabase('dne')
  File "pepex2.py", line 11, in __init__
    raise_from(DatabaseError('failed to open'), exc)
  File "/home/marc/.virtualenvs/scratch_future3/lib/python3.3/site-packages/future/utils/__init__.py", line 382, in raise_from
    exec(execstr, myglobals, mylocals)
  File "<string>", line 1, in <module>
__main__.DatabaseError: failed to open

Note that the traceback and exception information are missing from the FileNotFoundError.