Allow modules (and program blocks in particular) to nest.

An important advantage of program blocks is its ability to nest
within a module. This winds up also allowing modules to nest, which
is legal but presumably less used feature.

Module.cc

@@ -27,8 +27,8 @@
 list<Module::named_expr_t> Module::user_defparms;
 
 /* n is a permallocated string. */
-Module::Module(perm_string n)
-: PScopeExtra(n)
+Module::Module(LexicalScope*parent, perm_string n)
+: PScopeExtra(n, parent)
 {
       library_flag = false;
       is_cell = false;