Fixes #347.

* spot/twaalgos/minimize.cc, spot/twaalgos/minimize.hh: An SCC of the
determinized automaton is marked as accepting if it intersects any
accepting SCC of the original automaton.  This can be checked by
making a product.  As a consequence the output of minimize_wdba() now
always includes the original language, and minimize_obligation() only
needs a single containment check.
* NEWS: Mention this.