Extend candidate list for custom grep-files function with history

It might be useful to actually see the history entries, so let's
explicitly include them in the candiate list.

site-lisp/db-utils.el

@@ -536,14 +536,17 @@ entries, even if I want to use the input directly."
               (car grep-files-history)
               (car (car grep-files-aliases))))
          (files (completing-read
-                 (format "Search for \"%s\" in files matching wildcard: "
-                         regexp)
+                 (format "Search for \"%s\" in files matching wildcard (default: %s): "
+                         regexp
+                         default)
                  (delete-dups
                   (delq nil
                         (append (list default default-alias default-extension)
+                                grep-files-history
                                 (mapcar #'car grep-files-aliases))))
                  nil nil nil
-                 'grep-files-history)))
+                 'grep-files-history
+                 default)))
     (and files
          (or (cdr (assoc files grep-files-aliases))
              files))))