Don't squash markers in occur-edit-mode

Don't squash markers in occur-edit-mode

* lisp/replace.el (occur-after-change-function): Instead of replacing
the whole line being edited, use shrink-wrapping to replace the
smallest interval encompassing the change.  That way, we avoid
disturbing markers (such as occur highlighting locations) in the line;
they would otherwise all be forced to the beginning.