Prefer emplace_back to push_back

* spot/graph/ngraph.hh, spot/ltsmin/ltsmin.cc,
spot/misc/bitvect.hh, spot/misc/intvcomp.cc,
spot/misc/satsolver.cc, spot/priv/weight.cc,
spot/ta/taexplicit.cc, spot/taalgos/minimize.cc,
spot/taalgos/reachiter.cc, spot/tl/exclusive.cc,
spot/tl/formula.cc, spot/tl/formula.hh,
spot/tl/mark.cc, spot/tl/mutation.cc,
spot/tl/relabel.cc, spot/tl/remove_x.cc,
spot/tl/simplify.cc, spot/twa/acc.cc,
spot/twa/acc.hh, spot/twa/formula2bdd.cc,
spot/twa/taatgba.cc, spot/twa/taatgba.hh,
spot/twa/twa.hh, spot/twa/twagraph.cc,
spot/twaalgos/bfssteps.cc, spot/twaalgos/canonicalize.cc,
spot/twaalgos/compsusp.cc, spot/twaalgos/copy.cc,
spot/twaalgos/cycles.cc, spot/twaalgos/degen.cc,
spot/twaalgos/determinize.cc, spot/twaalgos/dtwasat.cc,
spot/twaalgos/emptiness.cc, spot/twaalgos/gv04.cc,
spot/twaalgos/hoa.cc, spot/twaalgos/ltl2taa.cc,
spot/twaalgos/ltl2tgba_fm.cc, spot/twaalgos/magic.cc,
spot/twaalgos/mask.hh, spot/twaalgos/minimize.cc,
spot/twaalgos/powerset.cc, spot/twaalgos/product.cc,
spot/twaalgos/randomgraph.cc, spot/twaalgos/reachiter.cc,
spot/twaalgos/relabel.cc, spot/twaalgos/remfin.cc,
spot/twaalgos/sccfilter.cc, spot/twaalgos/se05.cc,
spot/twaalgos/simulation.cc, spot/twaalgos/stutter.cc,
spot/twaalgos/tau03opt.cc, spot/twaalgos/totgba.cc,
spot/twaalgos/word.cc, tests/core/bitvect.cc: here.

spot/priv/weight.cc

@@ -52,7 +52,7 @@ namespace spot
     std::vector<unsigned> res;
     for (unsigned n = 0; n < max; ++n)
       if (m[n] > w.m[n])
-        res.push_back(n);
+        res.emplace_back(n);
     return acc_cond::mark_t(res.begin(), res.end());
   }