integers(min_value=0) always produces longs on Python 2

[DRMacIver]

>>> find(st.integers(min_value=0), lambda x: True)
0L

The underlying culprit seems to be that our floor and ceil functions in hypothesis.internal.compat always return long values. This is because we explicitly use _long_int_type. It's unclear that this is necessary - using int(x) will generally do the right thing for values that don't fit into an int.