vim-patch:7.4.248

Problem:    Cannot distinguish between NL and NUL in output of system().
Solution:   Add systemlist(). (ZyX)

https://code.google.com/p/vim/source/detail?r=v7-4-248
Return list from rettv_list_alloc.
vim-patch:7.4.256

Problem:    Using systemlist() may cause a crash and does not handle NUL
            characters properly.
Solution:   Increase the reference count, allocate memory by length. (Yasuhiro
            Matsumoto)

https://code.google.com/p/vim/source/detail?r=v7-4-256
Fix system() output truncation bug.

Replace NULs with SOH to restore the old behaviour of get_cmd_output().
Optimize get_system_output_as_rettv().