The reason behind this is that we can better control the behaviour
of the underlying configuration modules, such as the case for undefined
options or for quickly fixing other bugs. Another side effect of this
change is that it gets us closer to the moment where we will not
be dependent on logilab.common anymore, which will definitely
make our pytest users happy.
Some parts were copied almost verbatim from logilab.common.configuration
and logilab.common.optik_ext and pylint.config will definitely need
a refactoring and reengineering for abstracting the configuration,
so that we won't use optparse anymore, but that's subject for another
patch.
