Log when loading an invalid external module type

lib/msf/core/modules/external/shim.rb

@@ -18,8 +18,7 @@ class Msf::Modules::External::Shim
     when 'multi_scanner'
       multi_scanner(mod)
     else
-      # TODO have a nice load error show up in the logs
-      ''
+      nil
     end
   end
 

lib/msf/core/modules/loader/executable.rb

@@ -85,7 +85,13 @@ class Msf::Modules::Loader::Executable < Msf::Modules::Loader::Base
       return ''
     end
     begin
-      Msf::Modules::External::Shim.generate(full_path)
+      content = Msf::Modules::External::Shim.generate(full_path)
+      if content
+        return content
+      else
+        elog "Unable to load module #{full_path}, unknown module type"
+        return ''
+      end
     rescue ::Exception => e
       elog "Unable to load module #{full_path} #{e.class} #{e} #{e.backtrace.join "\n"}"
       # XXX migrate this to a full load_error when we can tell the user why the