Use org-string-match-p for backward compatibility with Emacs22

* org-freemind.el (org-freemind-convert-links-helper)
(org-freemind-convert-text-p, org-freemind-write-mm-buffer)
(org-freemind-get-node-style): Use org-string-match-p for backward
compatibility with Emacs22.

lisp/org-freemind.el

@@ -308,7 +308,7 @@ MATCHED is the link just matched."
   (let* ((link (match-string 1 matched))
          (text (match-string 2 matched))
          (ext (file-name-extension link))
-         (col-pos (string-match-p ":" link))
+         (col-pos (org-string-match-p ":" link))
          (is-img (and (image-type-from-file-name link)
                       (let ((url-type (substring link 0 col-pos)))
                         (member url-type '("file" "http" "https")))))
@@ -414,7 +414,7 @@ MATCHED is the link just matched."
 (defun org-freemind-convert-text-p (text)
   "Convert TEXT to html with <p> paragraphs."
   ;; (string-match-p "[^ ]" "  a")
-  (setq org-freemind-bol-helper-base-indent (string-match-p "[^ ]" text))
+  (setq org-freemind-bol-helper-base-indent (org-string-match-p "[^ ]" text))
   (setq text (org-freemind-escape-str-from-org text))
 
   (setq text (replace-regexp-in-string "\\([[:space:]]\\)\\(/\\)\\([^/]+\\)\\(/\\)\\([[:space:]]\\)" "\\1<i>\\3</i>\\5" text))
@@ -658,7 +658,7 @@ Otherwise give an error say the file exists."
 (defun org-freemind-write-mm-buffer (org-buffer mm-buffer node-at-line)
   (with-current-buffer org-buffer
     (dolist (node-style org-freemind-node-styles)
-      (when (string-match-p (car node-style) buffer-file-name)
+      (when (org-string-match-p (car node-style) buffer-file-name)
         (setq org-freemind-node-style (cadr node-style))))
     ;;(message "org-freemind-node-style =%s" org-freemind-node-style)
     (save-match-data
@@ -835,7 +835,7 @@ Otherwise give an error say the file exists."
     (dolist (style-list org-freemind-node-style)
       (let ((node-regexp (car style-list)))
         (message "node-regexp=%s node-name=%s" node-regexp node-name)
-        (when (string-match-p node-regexp node-name)
+        (when (org-string-match-p node-regexp node-name)
           ;;(setq node-style (org-freemind-do-apply-node-style style-list))
           (setq node-style (cadr style-list))
           (when node-style