app: allow plugin inside first-level directories of plug-ins folders.

We don't search recursively but only at the first level. If a plugin is
in its own subdirectory, the entry point has to be named the same (minus
extension) as the directory. For instance my-plugin/my-plugin for a
binary, or my-plugin/my-plugin.(py|exe|…).
This way, a plugin can load shared objects (libraries, other script
files, etc.) without polluting the main plug-ins directories, and in
particular without interfering with other plug-ins.
This is a first step to fix bug 757057 (DLL files which were used in
various plugins).

app/plug-in/gimppluginmanager-restore.c

@@ -278,6 +278,60 @@ gimp_plug_in_manager_search_directory (GimpPlugInManager *manager,
 
                   gimp_plug_in_manager_add_from_file (manager, child, mtime);
                 }
+              else if (g_file_query_file_type (child,
+                                               G_FILE_CREATE_NONE,
+                                               NULL) == G_FILE_TYPE_DIRECTORY)
+                {
+                  /* Search in subdirectory the first executable file with the
+                   * same name as the directory (except extension).
+                   * We don't search recursively, but only at a single level
+                   * and assume that there can be only 1 plugin inside a
+                   * directory.
+                   */
+                  GFileEnumerator *enumerator2;
+
+                  enumerator2 = g_file_enumerate_children (child,
+                                                           G_FILE_ATTRIBUTE_STANDARD_NAME ","
+                                                           G_FILE_ATTRIBUTE_STANDARD_IS_HIDDEN ","
+                                                           G_FILE_ATTRIBUTE_TIME_MODIFIED,
+                                                           G_FILE_QUERY_INFO_NONE,
+                                                           NULL, NULL);
+                  if (enumerator2)
+                    {
+                      GFileInfo *info2;
+
+                      while ((info2 = g_file_enumerator_next_file (enumerator2, NULL, NULL)))
+                        {
+                          if (! g_file_info_get_is_hidden (info2))
+                            {
+                              GFile *child2;
+                              gchar *file_name;
+                              char  *ext;
+
+                              child2 = g_file_enumerator_get_child (enumerator2, info2);
+                              file_name = g_strdup (g_file_info_get_name (info2));
+                              ext = strrchr (file_name, '.');
+                              if (ext)
+                                *ext = '\0';
+                              if (g_strcmp0 (file_name, g_file_info_get_name (info)) == 0 &&
+                                  gimp_file_is_executable (child2))
+                                {
+                                  guint64 mtime;
+
+                                  mtime = g_file_info_get_attribute_uint64 (info2,
+                                                                            G_FILE_ATTRIBUTE_TIME_MODIFIED);
+
+                                  gimp_plug_in_manager_add_from_file (manager, child2, mtime);
+                                  break;
+                                }
+                              g_object_unref (child2);
+                              g_free (file_name);
+                            }
+                          g_object_unref (info2);
+                        }
+                    }
+                  g_object_unref (enumerator2);
+                }
 
               g_object_unref (child);
             }