Disallow calling data() on rvalue Image and Trade::ImageData.

That would cause accessing freed data. Use release() instead (and then
you are on your own). The AbstractShaderProgram GL test now fails to
compile.

src/Magnum/Image.h

@@ -144,10 +144,24 @@ template<UnsignedInt dimensions> class Image {
          *
          * @see @ref release()
          */
-        Containers::ArrayView<char> data() { return _data; }
+        Containers::ArrayView<char> data()
+            #ifndef CORRADE_GCC47_COMPATIBILITY
+            &
+            #endif
+            { return _data; }
+        #ifndef CORRADE_GCC47_COMPATIBILITY
+        Containers::ArrayView<char> data() && = delete; /**< @overload */
+        #endif
 
         /** @overload */
-        Containers::ArrayView<const char> data() const { return _data; }
+        Containers::ArrayView<const char> data() const
+            #ifndef CORRADE_GCC47_COMPATIBILITY
+            &
+            #endif
+            { return _data; }
+        #ifndef CORRADE_GCC47_COMPATIBILITY
+        Containers::ArrayView<const char> data() const && = delete; /**< @overload */
+        #endif
 
         /** @overload */
         template<class T = char> T* data() {

src/Magnum/Trade/ImageData.h

@@ -221,10 +221,24 @@ template<UnsignedInt dimensions> class ImageData {
          *
          * @see @ref release()
          */
-        Containers::ArrayView<char> data() { return _data; }
+        Containers::ArrayView<char> data()
+            #ifndef CORRADE_GCC47_COMPATIBILITY
+            &
+            #endif
+            { return _data; }
+        #ifndef CORRADE_GCC47_COMPATIBILITY
+        Containers::ArrayView<char> data() && = delete; /**< @overload */
+        #endif
 
         /** @overload */
-        Containers::ArrayView<const char> data() const { return _data; }
+        Containers::ArrayView<const char> data() const
+            #ifndef CORRADE_GCC47_COMPATIBILITY
+            &
+            #endif
+            { return _data; }
+        #ifndef CORRADE_GCC47_COMPATIBILITY
+        Containers::ArrayView<const char> data() const && = delete; /**< @overload */
+        #endif
 
         /** @overload */
         template<class T> T* data() {