vim-patch:7.4.478: Use character lenght for 'showbreak'

vim-patch:7.4.478

Problem:    Using byte length instead of character length for
'showbreak'.
Solution:   Compute the character length. (Marco Hinz)

https://code.google.com/p/vim/source/detail?r=v7-4-478

src/nvim/version.c

@@ -188,7 +188,7 @@ static int included_patches[] = {
   //481,
   //480,
   //479,
-  //478,
+  478,
   //477,
   //476,
   //475,