Show a border around unfocused inline editors.

Now that we no longer show the "OK" and "Cancel" buttons for single-line inline
editors, it can be confusing when one edits the summary but no draft banner
appears because the editor hasn't been saved.

This change adds a red shadow on the outside of any text inputs which have lost
focus, to indicate that something's not saved.

Testing done: Checked out the new border.

Fixes bug 3242.

Reviewed at https://reviews.reviewboard.org/r/5631/