introduced Project/Package checkout descriptor
With the new checkout descriptor it is possible to write something like:
gaudi = Project('Gaudi', 'HEAD')
gaudi.checkout = 'git'
gaudi.checkout()
or
gaudi = Project('Gaudi', 'HEAD')
gaudi.checkout = ('git',
{'url': 'http://git.examples.org/Gaudi.git',
'commit': 'new_feature'})
gaudi.checkout()