Tests for vertical splits and filler lines in diff mode

STARTTEST
:so small.vim
/^1
yG:new
pkdd:w! Xtest
ddGpkkrXoxxx:w! Xtest2
:file Nop
ggoyyyjjjozzzz
:vert diffsplit Xtest
:vert diffsplit Xtest2
:" jump to second window for a moment to have filler line appear at start of
:" first window
ggpgg:let one = winline()
j:let one = one . "-" . winline()
j:let one = one . "-" . winline()
j:let one = one . "-" . winline()
j:let one = one . "-" . winline()
j:let one = one . "-" . winline()
gg:let two = winline()
j:let two = two . "-" . winline()
j:let two = two . "-" . winline()
j:let two = two . "-" . winline()
j:let two = two . "-" . winline()
gg:let three = winline()
j:let three = three . "-" . winline()
j:let three = three . "-" . winline()
j:let three = three . "-" . winline()
j:let three = three . "-" . winline()
j:let three = three . "-" . winline()
j:let three = three . "-" . winline()
:call append("$", one)
:call append("$", two)
:call append("$", three)
:$-2,$w! test.out
:qa!
ENDTEST

1 aa
2 bb
3 cc
4 dd
5 ee