Merge remote-tracking branch 'xlrd' into py2.6

Conflicts:
	xlrd/timemachine.py
Remove miscellaneous workarounds for pre-2.6 Python

* nested scopes enabled in 2.2
* object() introduced in 2.2
* True and False added in 2.3
Remove ZipFile.open() workaround for pre-2.6 Python
Remove pre-2.6 Python workarounds from setup.py

* dict() keyword arguments supported since 2.3
* dict.update() keyword arguments allowed since 2.4