Add a script for updating gnome-desktop sources

Nautilus depends on thumbnail source code files from the gnome-desktop project. Therefore, when the upstream https://gitlab.gnome.org/GNOME/gnome-desktop project releases a new version of the files, they should be downloaded and merged into the nautilus project.

The script downloads the latest gnome-desktop project files to the developer's local nautilus source folder so that the developer can commit the updated files to the nautilus project.

Fixes: #839

.gitattributes

@@ -1,10 +1,11 @@
-/.gitattributes                export-ignore
-/.gitignore                    export-ignore
-/.gitmodules                   export-ignore
-/nautilus.doap                 export-ignore
-/docs/Overview.md              export-ignore
-/test/file-torture.py          export-ignore
-/src/gtk/gtk-code-generator.sh export-ignore
-/data/run-uncrustify.sh        export-ignore
-/data/uncrustify.cfg           export-ignore
-/build-aux/make_release.sh     export-ignore
+/.gitattributes                             export-ignore
+/.gitignore                                 export-ignore
+/.gitmodules                                export-ignore
+/nautilus.doap                              export-ignore
+/docs/Overview.md                           export-ignore
+/test/file-torture.py                       export-ignore
+/src/gnome-desktop/gnome-desktop-update.sh  export-ignore
+/src/gtk/gtk-code-generator.sh              export-ignore
+/data/run-uncrustify.sh                     export-ignore
+/data/uncrustify.cfg                        export-ignore
+/build-aux/make_release.sh                  export-ignore

src/gnome-desktop/gnome-desktop-update.sh

@@ -0,0 +1,45 @@
+#!/bin/sh
+#
+# gnome-desktop-update.sh
+#
+# Fetch the latest master gnome-desktop-thumbnail source code from the
+# gnome-desktop project https://gitlab.gnome.org/GNOME/gnome-desktop
+#
+# The Nautilus gnome-desktop thumbnail code directly tracks the gnome-desktop
+# repository. There is typically no need to modify the received files.
+#
+# Usage:
+#
+# Execute the script within the nautilus/src/gnome-desktop directory.
+# For example:
+#
+# $ cd src/gnome-desktop
+# $ ./gnome-desktop-update.sh
+#
+
+URL=https://gitlab.gnome.org/GNOME/gnome-desktop/raw/master/libgnome-desktop/
+FILES=(
+    "gnome-desktop-thumbnail.c"
+    "gnome-desktop-thumbnail.h"
+    "gnome-desktop-thumbnail-script.c"
+    "gnome-desktop-thumbnail-script.h"
+)
+r=0
+
+for f in ${FILES[@]}; do
+  echo "GET: $URL$f"
+  if curl -sfO $URL$f; then
+    echo " OK: $f"
+  else
+    echo "ERR: $f download error."
+    r=1
+  fi;
+done
+
+if [ $r -eq 0 ]; then
+  echo "SUCCESS: All updates completed successfully."
+else
+  echo "WARNING: One or more updates encountered an error."
+fi;
+
+exit $r