Issue #50: Show file permission differences

Added variable ztree-diff-consider-file-permissions (turned off
by default) which controls whether file permissions shall
be taken into consideration when comparing files.

README.md

@@ -58,6 +58,8 @@ By default all files starting with dot (like `.gitignore`) are not shown and exc
 
 One also could turn on unicode characters to draw the tree with instead of normal ASCII-characters. This is controlled by the `ztree-draw-unicode-lines` variable.
 
+The variable `ztree-diff-consider-file-permissions` (which is `nil` by default) if set to `t` allows to compare file attributes as well, the files will be considered different if they have different mode.
+
 ### Screenshots
 
 ![ztreediff emacsx11](https://github.com/fourier/ztree/raw/screenshots/screenshots/emacs_diff_xterm.png "Emacs in xterm with ztree-diff")

ztree-diff-model.el

@@ -33,6 +33,9 @@
 (require 'ztree-util)
 (eval-when-compile (require 'cl-lib))
 
+(defvar ztree-diff-consider-file-permissions nil
+  "Mark files as different if their permissions are different")
+
 (defvar-local ztree-diff-model-ignore-fun nil
   "Function which determines if the node should be excluded from comparison.")
 
@@ -147,7 +150,10 @@ Returns t if equal."
          (file2-untrampified (ztree-untrampify-filename file2)))
     (if (or
          (/= (nth 7 (file-attributes file1))
-            (nth 7 (file-attributes file2)))
+             (nth 7 (file-attributes file2)))
+         (and ztree-diff-consider-file-permissions
+              (not (string-equal (nth 8 (file-attributes file1))
+                                 (nth 8 (file-attributes file2)))))
          (/= 0 (process-file diff-command nil nil nil "-q"
                            file1-untrampified
                            file2-untrampified)))