Optimize chains of assignments

This allows optimizing, for example:

  integer a = 1;
  integer b = a;
  llOwnerSay((string)b);

which wasn't done before. This case is prone to happen with inlined functions, e.g. using the result of an inlined function as a parameter to another.

lslopt/lsldeadcode.py

@@ -318,6 +318,15 @@ class deadcode(object):
 
             node = sym['W']
             nt = node.nt
+
+            while nt == 'IDENT':
+                # Follow the chain of identifiers all the way to the original
+                if self.symtab[node.scope][node.name].get('W', False) is False:
+                    return sym
+                sym = self.symtab[node.scope][node.name]
+                node = sym['W']
+                nt = node.nt
+
             if nt == 'CONST':
                 tcurnode = curnode.t
                 if tcurnode in ('integer', 'string', 'key'):