gen_integer() change

Using Win64 Python2.7, sys.maxsize returns a long and the `isinstance(maxsize, int)` test fails. I updated this to a tuple to consider the differences with Python3 (which doesn't really use `long()`) by adding an integer types tuple `(int, long,)` depending on the platform.
I am finally at my computer now and was thinking, how using:

```python
if sys.version_info.major < 3:
```

I only now realized that ``sys.version`` returns a string and I feel that comparing a string is a bit weird...

```python
sys.version
'2.7.6 (default, Sep  9 2014, 15:04:36) \n[GCC 4.2.1 Compatible Apple LLVM 6.0 (clang-600.0.39)]'
```