[RP] inaccessible frames

[Rupert Levene]

If you follow the steps below you end up with inaccessible frames,
which I've labelled with '?'. Should ratpoison try to check for such
problems when you remove a frame, and try an alternative strategy? In
this example, rather than enlarging C, frame B should be enlarged to
fill the space left by removing D after the first step.

Rupert

---------
|   | B |
| A |---|
|   |   |
|---| D |  <-- remove D
| C |   |
---------

---------
|   | B |  <-- remove B
| A |---|
|   | ? |
|-------|
|   C   |
---------

---------
|   |   |
| A | ? |
|   |   |
|-------|
|   C   | <-- remove C
---------

---------
|   |   |
|   |   |
| A | ? | <-- A is the only frame
|   |   |
|   |   |
---------