updated changelog for 2.6.0 release
updated changelog for 2.6.0 release

Instead of a 2.5.1 release, add in the absolute tempurl option to the release and bump it to 2.6.0

Change-Id: Ie8335a737aac3211a240c25d88501f8f5dbccbea

jeseem/python-swiftclient,jeseem/python-swiftclient,openstack/python-swiftclient,VyacheslavHashov/python-swiftclient,ironsmile/python-swiftclient,openstack/python-swiftclient,ironsmile/python-swiftclient,sohonetlabs/python-swiftclient,sohonetlabs/python-swiftclient,VyacheslavHashov/python-swiftclient