* src/tgbaalgos/sccfilter.cc: tgba_explicit_numbered replace
tgba_explicit_string for the general case.  This way we don't have to
prefix the result of format_state() in case to states have the same
description.  We just number the states instead.  For the specific
cases where the input automata are instance of tgba_explicit_string or
tgba_explicit_formula, we clone the label.