Rendering gdb tui mode seems broken

[herrhotzenplotz]

I guess this one is pretty obvious:

Steps to reproduce:

$ gdb -q -tui --args ./foobar

[christianparpart]

I in fact had to check how it is supposed to look like.

There are two problems to be fixed:

• box-drawing not showing the expected characters (maybe due to shift-select VT sequences?)
• background color should have been cleared, but isn't?

That's urgent enough, IMHO, i'll fix that right after i'm done with selection PR.

[whisperity]

Affects more than just gdb tui. aptitude:

[christianparpart]

All fixed on master.