src/ltm.js: Fix luaT_objtypename
src/ltm.js: Fix luaT_objtypename

  - it tried to index the tvalue instead of the metatable
  - it returns a jsstring in __name case, but lua string in fallback

dlbd/fengari,daurnimator/fengari,fengari-lua/fengari,giann/fengari