disable usage of _PyType_Lookup() in Py<=2.6/3.1

--HG--
extra : amend_source : c827dfd2e781c1a7e1b982601b6ee8e826d5b4ed
split withstat_py test to make the compatible part run in Py26

--HG--
rename : tests/run/withstat_py.py => tests/run/withstat_py27.py
add context manager test with threading.Lock which previously failed in Py2.6 (by Wouter Bolsterlee)
Add date to release notes.
optimise set(it) into a call to PySet_New(it)
fix repeated list multiplication

--HG--
extra : amend_source : 2797e0ad678cc0a33a2548a8a20b00475bc8a21b

Conflicts:
	CHANGES.rst
Merge branch 'master' into 0.20.x

Conflicts:
	CHANGES.rst
0.20.1rc1
optimise frozenset(it) into a call to PyFrozenSet_New(it)
fix Py2.4 compatibility definition of PyFrozenSet_New(it)
tutorial for Python arrays
Bump version for release.
Merge branch 'master' of github.com:cython/cython
Bump version.
changelog
merge 0.20.x branch into master
add missing ";" in C code
merge 0.20.x branch into master
Support for C++ unordered sets and maps.
Allow distutils directives in test files.