When we consider if a path has been totally rewritten, we did not
touch changes from symlinks to files or vice versa. But a change
that modifies even the type of a blob surely should count as a
complete rewrite.
While we are at it, modernise diffcore-break to be aware of gitlinks (we
do not want to touch them).
Signed-off-by: Junio C Hamano <gitster@pobox.com>
