CPack: initial commit.

Add the simplest CPack configuration for
'make package' and 'make package_source'
targets.
Add an empty snapshot to revision control
to use in 'make package' and thus
spare the user from the need to do
--init-storage.
Modify args.test to accept a bare
(no git version) version number, and thus
ensure the user from a yet another call before
he/she can start work/play around.