bug#47701: Add ln --dry-run

[積丹尼 Dan Jacobson]

$ ln -rbsv ~/Downloads/*/95*[0-9].jpg xiangpianjibentu
'xiangpianjibentu/95212025.jpg' -> 
'../../../../Downloads/NNNNViewLarge_Draw_files/95212025.jpg'
'xiangpianjibentu/95212033.jpg' -> 
'../../../../Downloads/ViecccwLarge_Draw_files/95212033.jpg'
'xiangpianjibentu/95212025.jpg~' ~ 'xiangpianjibentu/95212025.jpg' -> 
'../../../../Downloads/ViewLarge_Draw_files/95212025.jpg'
'xiangpianjibentu/95212026.jpg' -> 
'../../../../Downloads/ViewLargeddd_Draw_files/95212026.jpg'
'xiangpianjibentu/95212034.jpg' -> 
'../../../../Downloads/ViewLargvvve_Draw_files/95212034.jpg'
'xiangpianjibentu/95212045.jpg' -> 
'../../../../Downloads/ViewxxxLarge_Draw_files/95212045.jpg'

Wow, that was a pretty fancy result.

However the only way to find out what will happen is to cross one's
fingers and run the command and hope for the best.

So perhaps add a --dry-run.

It would print (when -v is used), but not do, the above.

(Except probably for the one backup file.)

Anyway, we all know that sometimes ln syntax is tricky,
so perhaps add --dry-run.