* src/tgba/tgbaexplicit.hh: Rerganize a bit to
allow different functions to be used to format
states.  Add an enabled_utf8() method to
tgba_explicit_formula.
* src/tgbaalgos/dotty.hh, src/tgbaalgos/dotty.cc:
Simplify the interface by not depending on
dotty_decorator explicitely.
* src/tgba/bddprint.hh (enable_utf8): New function.
* src/tgba/bddprint.cc (enable_utf8): Implement it
and use the global utf8 flag in other functions.
* src/tgbatest/ltl2tgba.cc: Add an -8 option for
UTF-8 outpout.
* wrap/python/spot.i: Adjust for tgbexplicit.hh
changes.