BF: make integer tests safe for python 2

Longs can appear in place of integers, especially on Windows.  Use
compatible test for (int, long) or (int,) depending on python version.
RF: use abstract base class for integer check

Use numbers.Integer base class to check for integer instances.
DOC: update python and library dependencies

We depend on Python 2.6 and pydicom 0.9.7.
Merge pull request #223 from matthew-brett/int-long-check-fix

BF: make integer tests safe for python 2

Longs can appear in place of integers, especially on Windows. Use compatible
test for (int, long) or (int,) depending on python version.