fix and check shifting issue

The exception raised by << and >> when shifting mark_t by too many
bits are only enabled in SPOT_DEBUG, as those operations are quite
low-level.  However we were always testing them, and although we
wanted them to be active in Python, it was not always the case.

* spot/twa/acc.hh: introduce max_accsets() as
a static constexpr method, so we can see it in Python.
* spot/misc/bitset.hh: Fix preprocessing directive
so the check is actually enabled when compiling the Python
bindings.
* bin/autcross.cc, bin/autfilt.cc, bin/ltlcross.cc: Use max_accsets().
* tests/core/acc.cc: Comment out the shifting exception when
SPOT_DEBUG is unset.
* tests/python/except.py: Make sure the exception is always raised in
Python.

bin/ltlcross.cc

@@ -691,7 +691,8 @@ namespace
                    const spot::const_twa_graph_ptr& aut_j,
                    size_t i, size_t j, bool icomp, bool jcomp)
   {
-    if (aut_i->num_sets() + aut_j->num_sets() > SPOT_MAX_ACCSETS)
+    if (aut_i->num_sets() + aut_j->num_sets() >
+        spot::acc_cond::mark_t::max_accsets())
       {
         // Report the skipped test if both automata are not
         // complemented, or the --verbose option is used,