bug#13130: 24.2.90; :box face attribute problems

[Dmitry Gutov <dgutov@yandex.ru>]

I'd like to use this attribute on the face that yasnippet sets on active
field overlays. So, to reproduce:

1. Install yasnippet.

2. Eval this:

(let ((color (face-attribute 'region :background)))
  (defface yas-field-highlight-box
    `((t :box (:line-width -1 :color ,color)))
    "Box the color of region."))
    
(put 'yas-field-highlight-face 'face-alias 'yas-field-highlight-box)

3. Open a buffer, M-x ruby-mode, type "forin", press Tab.

Problems:
a) Despite line-width of -1, the character widths are still affected.
You can observe it when tabbing between the fields: as the field becomes
inactive, it shrinks in width a bit.

b) The box border is drawn not only around the overlay, but also around
all pieces of text with different faces inside it. To reproduce, type
this in one of the fields: "abc"[/b/]

If installing yasnippet is a problem, I can try to localize the bug with
a smaller example.

--Dmitry

In GNU Emacs 24.2.90.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.6.0)
 of 2012-11-26 on vbx
Bzr revision: 110959 rgm@gnu.org-20121126014100-0199uq4y2fo0cnaz
Windowing system distributor `The X.Org Foundation', version 11.0.11300000
System Description:	Ubuntu 12.10