- open ports tree patches in diff-mode.

Index: lisp/files.el
--- lisp/files.el.orig
+++ lisp/files.el
@@ -2992,6 +2992,7 @@ ARC\\|ZIP\\|LZH\\|LHA\\|ZOO\\|[JEW]AR\\|XPI\\|RAR\\|CB
      ("\\.\\(as\\|mi\\|sm\\)2\\'" . snmpv2-mode)
      ("\\.\\(diffs?\\|patch\\|rej\\)\\'" . diff-mode)
      ("\\.\\(dif\\|pat\\)\\'" . diff-mode) ; for MS-DOS
+     ("/patch-[^/]*$" . diff-mode)
      ("\\.[eE]?[pP][sS]\\'" . ps-mode)
      ("\\.\\(?:PDF\\|EPUB\\|CBZ\\|FB2\\|O?XPS\\|DVI\\|OD[FGPST]\\|DOCX\\|XLSX?\\|PPTX?\\|pdf\\|epub\\|cbz\\|fb2\\|o?xps\\|djvu\\|dvi\\|od[fgpst]\\|docx\\|xlsx?\\|pptx?\\)\\'" . doc-view-mode-maybe)
      ("configure\\.\\(ac\\|in\\)\\'" . autoconf-mode)