Disallow copy for security.

* src/tgba/tgbabddconcrete.hh (tgba_bdd_concrete): Disallow copy.
* src/tgba/tgbaexplicit.hh (tgba_explicit): Likewise.
* src/tgba/tgbaexplicit.cc (tgba_explicit::operator=,
tgba_explicit::tgba_explicit(tgba_explicit)): Remove.
* src/tgba/tgbabddconcreteproduct.cc
(tgba_bdd_concrete_product_factory::tgba_bdd_concrete_product_factory,
product): Take operand automata as pointers.
* src/tgba/tgbabddconcreteproduct.hh (product): Likewise.
* src/tgba/tgbaproduct.cc, src/tgba/tgbaproduct.hh:
(tgba_product): Disallow copy.
(tgba_product::tgba_product): Take operand automata as pointers.
* src/tgbaalgos/dotty.cc (dotty_state, dotty_rec, dotty_reachable):
Take tgba arguments as pointer.
* src/tgbaalgos/dotty.hh (dotty_reachable): Likewise.
* src/tgbaalgos/lbtt.cc (fill_todo, lbtt_reachable): Likewise.
* src/tgbaalgos/lbtt.hh (lbtt_reachable): Likewise.
* src/tgbaalgos/ltl2tgba.cc, src/tgbaalgos/ltl2tgba.hh (ltl_to_tgba):
Likewi...