improve compatibility for python 3

- correct .travis.yml
- make TransformerIterator iterable
- remove comparison "None > 0"
- use six.text_type instead of unicode
- use six.moves.input instead of raw_input
- use six.moves.reduce
- use operator module instead of lambda function
- integer conversion
- convert the pretrained test data
- remove some unused import
Because `range` (equivalent to `xrange` in Python 2) takes integer arguments only in Python 3, casting to integer is required.

    ======================================================================
    ERROR: test_probabilistic_max_pooling.test_max_pool_channels
    ----------------------------------------------------------------------
    Traceback (most recent call last):

    ...

    File "/home/travis/build/euphoris/pylearn2/pylearn2/expr/probabilistic_max_pooling.py", line 627, in max_pool_channels_python
        for i in xrange(0, n / pool_size):
    TypeError: 'float' object cannot be interpreted as an integer