Fixed #162 (GDS2 libname not maintained)

Changelog

@@ -1,3 +1,8 @@
+0.25.5          (xxxx-xx-xx):
+
+* Bugfix: https://github.com/klayoutmatthias/klayout/issues/162
+       GDS2 LIBNAME was not maintained on "File/Save".
+
 0.25.4          (2018-08-25):
 * Bugfix: https://github.com/klayoutmatthias/klayout/issues/121
        Issue with multiple reads of GDS2 layouts including PCells

src/lay/lay/layMainWindow.cc

@@ -3170,6 +3170,8 @@ MainWindow::do_save (bool as)
           options.set_dbu (cv->layout ().dbu ());
           options.set_format_from_filename (fn);
 
+          cv->update_save_options (options);
+
           tl::OutputStream::OutputStreamMode om = tl::OutputStream::OM_Auto;
 
           if (as && ! mp_layout_save_as_options->get_options (current_view (), cv_index, fn, om, options)) {

src/laybasic/laybasic/layCellView.cc

@@ -258,6 +258,31 @@ LayoutHandle::set_save_options (const db::SaveLayoutOptions &options, bool valid
   m_save_options_valid = valid;
 }
 
+void
+LayoutHandle::update_save_options (db::SaveLayoutOptions &options)
+{
+  for (tl::Registrar<lay::PluginDeclaration>::iterator cls = tl::Registrar<lay::PluginDeclaration>::begin (); cls != tl::Registrar<lay::PluginDeclaration>::end (); ++cls) {
+
+    const lay::StreamWriterPluginDeclaration *decl = dynamic_cast <const lay::StreamWriterPluginDeclaration *> (&*cls);
+    if (! decl) {
+      continue;
+    }
+
+    std::auto_ptr<db::FormatSpecificWriterOptions> specific_options;
+    if (options.get_options (decl->format_name ())) {
+      specific_options.reset (options.get_options (decl->format_name ())->clone ());
+    } else {
+      specific_options.reset (decl->create_specific_options ());
+    }
+
+    if (specific_options.get ()) {
+      decl->initialize_options_from_layout_handle (specific_options.get (), *this);
+      options.set_options (specific_options.release ());
+    }
+
+  }
+}
+
 void 
 LayoutHandle::save_as (const std::string &fn, tl::OutputStream::OutputStreamMode om, const db::SaveLayoutOptions &options, bool update)
 {

src/laybasic/laybasic/layCellView.h

@@ -234,6 +234,15 @@ public:
     return m_save_options;
   }
 
+  /**
+   *  @brief Updates the given save options with attributes from this cell view
+   *
+   *  Some formats will initialize attributes from the cell view and the layout's
+   *  metadata (example: libname of GDS2). This method will update the options
+   *  if the layout provides attributes for initializing the latter.
+   */
+  void update_save_options (db::SaveLayoutOptions &options);
+
   /**
    *  @brief Gets a flag indicating whether the save options are valid
    *