FEAUTRE-REQUEST: upon git difftool, files which cannot be modified (persistently) should be made read only

Hi.

Apparently since a while, git difftool has the awseome feature, that it just symlinks the files to the working copy, if a diff with that is requested.

e.g. something like: git difftool -d will have /tmp/git-difftool.TWYTA

created with subdirs

left: -rw-r--r-- 1 user user 45k Oct 16 04:33 file

right: lrwxrwxrwx 1 calestyo calestyo 52 Oct 16 04:33 file -> /home/user/foo/file

When one edits and saves this in one's favourite difftool,... it actually gets into the working copy.

But of course saving the left (in this example) has no effect, so it would be nice if all these files were marked readonly, so that one already sees in the difftool "changes here are useless".

Cheers, Chris.