Another way to compile goto's

The compilation of a goto or a label just create an entry and generate
boilerplate code for the gotos. As we don't know yet whether it needs a
CLOSE, we code a jump followed by a CLOSE, which is then dead code.

When a block ends (and then we know for sure whether there are variables
that need to be closed), we check the goto's against the labels of that
block. When closing a goto against a label, if it needs a CLOSE, the
compiler swaps the order of the jump and the CLOSE, making the CLOSE
active.

testes/db.lua

@@ -128,7 +128,7 @@ then
 else
   a=2
 end
-]], {2,3,4,7})
+]], {2,4,7})
 
 
 test([[