* Never ever ever raise "tuple is not array" from CALL
* Support ALL use-cases from #291 (Seriously!)
* Add test cases for #1167
* Remove buggy luaL_isarray()
* Extract tuple_to_mpstream()
* Optimize luamp_encode_tuple() to use tuple_to_mpstream()
* Other performance optimizations

This code shouldn't introduce perfomance regression because
it still does the same number of operations for all use cases.