Add compiler support for `celldefine, vpiCellInstance

This patch adds support to the compiler and stub backend for
`celldefine. This matches the compiler portion of the full
support that was added to 0.10.devel. This does not change
vvp or the vvp interface since changing the interface is not
allowed in a stable branch.

Module.cc

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1998-2008 Stephen Williams ([email protected])
+ * Copyright (c) 1998-2009 Stephen Williams ([email protected])
  *
  *    This source code is free software; you can redistribute it
  *    and/or modify it in source code form under the terms of the GNU
@@ -29,6 +29,7 @@ Module::Module(perm_string n)
 : PScope(n)
 {
       library_flag = false;
+      is_cell = false;
       default_nettype = NetNet::NONE;
 }