app, libgimp, pdb: improve a bit gimp_image_get_parasite_list() docs.

It is more accurate to say it returns a list of parasite names rather
than a list of parasites (as we could take it as meaning a list of
GimpParasite). Of course, we would soon see the actual element contents
(if not for the introspection metadata (element-type gchar*)), but
better being accurate in textual docs too.

app/pdb/image-cmds.c

@@ -5558,7 +5558,7 @@ register_image_procs (GimpPDB *pdb)
                                "gimp-image-get-parasite-list");
   gimp_procedure_set_static_help (procedure,
                                   "List all parasites.",
-                                  "Returns a list of all currently attached parasites.",
+                                  "Returns a list of the names of all currently attached parasites. These names can later be used to get the actual #GimpParasite with 'gimp-image-get-parasite' when needed.",
                                   NULL);
   gimp_procedure_set_static_attribution (procedure,
                                          "Marc Lehmann",

libgimp/gimpimage_pdb.c

@@ -3385,7 +3385,9 @@ gimp_image_get_parasite (GimpImage   *image,
  *
  * List all parasites.
  *
- * Returns a list of all currently attached parasites.
+ * Returns a list of the names of all currently attached parasites.
+ * These names can later be used to get the actual #GimpParasite with
+ * gimp_image_get_parasite() when needed.
  *
  * Returns: (array length=num_parasites) (element-type gchar*) (transfer full):
  *          The names of currently attached parasites.

pdb/groups/image.pdb

@@ -2878,7 +2878,11 @@ CODE
 
 sub image_get_parasite_list {
     $blurb = 'List all parasites.';
-    $help  = 'Returns a list of all currently attached parasites.';
+    $help = <<'HELP';
+Returns a list of the names of all currently attached parasites.
+These names can later be used to get the actual #GimpParasite with
+gimp_image_get_parasite() when needed.
+HELP
 
     &marc_pdb_misc('1999', '2.8');