* src/ltlast/atomic_prop.cc, src/ltlast/automatop.cc,
src/ltlast/binop.cc, src/ltlast/bunop.cc, src/ltlast/constant.cc,
src/ltlast/formula.cc, src/ltlast/formula.hh,
src/ltlast/multop.cc, src/ltlast/unop.cc: Add a bit is.sere_formula
to track SEREs, and fix tracking of PSL formulae.
* src/ltltest/kind.test: Adjust.