Add optimizer option 'listlength' to optimize llGetListLength.

llGetListLength(arg) was transformed to arg!=[] whenever constant folding was active. This option allows disabling that optimization.

lslopt/lslfoldconst.py

@@ -1001,7 +1001,7 @@ class foldconst(object):
                                 warning(u"Can't optimize call to %s because it would generate a tab character (you can force the optimization with the 'foldtabs' option, or disable this warning by disabling the 'warntabs' option)." % node['name'].decode('utf8'))
                             return
                     parent[index] = {'nt':'CONST', 't':node['t'], 'value':value, 'SEF':True}
-                elif node['name'] == 'llGetListLength':
+                elif self.optlistlength and node['name'] == 'llGetListLength':
                     # Convert llGetListLength(expr) to (expr != [])
                     node = {'nt':'CONST', 't':'list', 'value':[]}
                     parent[index] = node = {'nt':'!=', 't':'list', 'ch':[child[0], node]}