Allow using add-face-text-property.

* helm-lib.el (helm-add-face-text-properties): New
* helm-grep.el (helm-grep-highlight-match):     Use it.
* helm.el (helm-fuzzy-default-highlight-match): Use it.

helm-grep.el

@@ -1100,7 +1100,7 @@ in recurse, and ignore EXTS, search being made recursively on files matching
                    (while (and (re-search-forward reg nil t)
                                (> (- (setq end (match-end 0))
                                      (setq beg (match-beginning 0))) 0))
-                     (add-text-properties beg end '(face helm-grep-match)))
+                     (helm-add-face-text-properties beg end 'helm-grep-match))
                    do (goto-char (point-min))) 
           (buffer-string))
       (error nil))))

helm-lib.el

@@ -76,6 +76,18 @@ much more convenient to use a simple boolean value here."
 (defvar helm-suspend-update-flag nil)
 (defvar helm-action-buffer "*helm action*"
   "Buffer showing actions.")
+
+
+;;; Compatibility
+;;
+(defun helm-add-face-text-properties (beg end face &optional append object)
+  "Add the face property to the text from START to END.
+It is a compatibility function which behave exactly like
+`add-face-text-property' is available otherwise like `add-text-properties'.
+When only `add-text-properties' is available APPEND is ignored."
+  (if (fboundp 'add-face-text-property)
+      (add-face-text-property beg end face append object)
+      (add-text-properties beg end `(face ,face) object)))
 
 ;;; Macros helper.
 ;;

helm.el

@@ -3083,8 +3083,8 @@ to the matching method in use."
               ;; Try first matching against whole pattern.
               (while (re-search-forward regex nil t)
                 (cl-incf count)
-                (add-text-properties
-                 (match-beginning 0) (match-end 0) '(face helm-match)))
+                (helm-add-face-text-properties
+                 (match-beginning 0) (match-end 0) 'helm-match))
               ;; If no matches start matching against multiples or fuzzy matches.
               (when (zerop count)
                 (cl-loop with multi-match = (string-match-p " " helm-pattern)
@@ -3097,16 +3097,16 @@ to the matching method in use."
                          if multi-match do
                          (progn
                            (while (re-search-forward p nil t)
-                             (add-text-properties
+                             (helm-add-face-text-properties
                               (match-beginning 0) (match-end 0)
-                              '(face helm-match)))
+                              'helm-match))
                            (goto-char (point-min)))
                          ;; Fuzzy matches (literal patterns).
                          else do
                          (when (search-forward p nil t)
-                           (add-text-properties
+                           (helm-add-face-text-properties
                             (match-beginning 0) (match-end 0)
-                            '(face helm-match))))))
+                            'helm-match)))))
           (invalid-regexp nil))
         ;; Now replace the original match-part with the part
         ;; with face properties added.