bug#67563: 30.0.50; Box should not extend with line-spacing

[Yuan Fu]

If I set a box face for a button, and then set a line-space for the buffer, I 
expect the extra space between lines to be added outside of the box, like so:

+-------------------------+
|          Box            |
|                         |
+-------------------------+
       extra line space
+-------------------------+
|          Box            |
|                         |
+-------------------------+

However, right now, the bottom line of the box includes the extra line spacing, 
like so:

+-------------------------+
|          Box            |
|                         |
+                         +
|      extra line space   |
+-------------------------+
+-------------------------+
|          Box            |
|                         |
+-------------------------+

Screenshot:

Ideally there should be some space between the two buttons on the two lines. 
Also notice the extra space above the bottom line of the box.

I also attached a repo file to produce these buttons.

If someone can give me some pointers, I can try to look into this.

Yuan

repo.el
Description: Binary data