Stop creating new lua_State for each function call. At least for C functions.

[Gerold103]

Call of _func functions creates a new lua_State via luaT_newthread(), and moves all the arguments to it. This is slow, probably very slow, but nobody measured properly. Should be most visible on C functions.

The new lua_State is not really needed - all can be done on the provided lua_State. For example, lbox_func_call() has a lua_State with all its arguments in it. No need to move them to a new state.

Why it is not done now I think is because port_lua does not support dumping not the entire lua_State. See encode_lua_call(). On the other hand the first argument is often a callable object (box.func.<name>, for example), which can't be popped from the stack (may trigger its GC). So an offset 1 would solve the problem.

The same will happen for the upcoming cbox module for calling C functions without touching the schema.