Merge branch 'jk/difftool-no-overwrite-on-copyback'

Try to be careful when difftool backend allows the user to write into the temporary files being shown *and* the user makes changes to the working tree at the same time. One of the changes has to be lost in such a case, but at least tell the user what he did. * jk/difftool-no-overwrite-on-copyback: t7800: run --dir-diff tests with and without symlinks t7800: fix tests when difftool uses --no-symlinks t7800: don't hide grep output difftool: don't overwrite modified files t7800: move '--symlinks' specific test to the end