Set cursor focus on several adminpages

[Carlos]

Suggestions for saving mouse clicks :-)

- On the Login page (/admin/index.php), set focus to Username form field.

- When editing pages (/admin/edit.php), if creating new page, set focus to Title field; if editing and existing one, set focus to Content (or don't set it).

I've made a pair of simple plugins that do this (login and page create), but I think it would to be nice to have that in the core.