add test files: {error,}-unknown1.sfp
allow unknown value
add unknown-{goal,init}.sfp
fix bugs for True/False constraints
allow unknown value in initial state
rename unknown-{init,goal}.sfp -> unknown1-{init,goal}; add test files unknown2-{init,goal}.sfp
unify TTBD + TUnknown = TAny
add test files for nothing value
add test files to good-test-files.txt; update test-ocaml.sh
enable nothing value