Suggestion: make git checkout safer

Currently a plain 'git checkout .' will revert any local changes, e.g.

    % mkdir test
    % cd test
    % git init
    Initialized empty Git repository in /home/eda/test/.git/
    % echo hello >foo
    % git add foo
    % git commit -m.
    [master (root-commit) 34f6694] .
     1 file changed, 1 insertion(+)
     create mode 100644 foo
    % echo goodbye >foo
    % git checkout .
    % cat foo
    hello

I suggest this is dangerous and by default 'git checkout' should only alter files which do not have local changes (as would be reported by 'git diff'). Only if --force is given should working tree differences be thrown away.

    % git --version
    git version 2.4.0