[RFC] vim-patch:7.4.323

Problem:    Substitute() with zero width pattern breaks multi-byte character.
Solution:   Take multi-byte character size into account. (Yukihiro Nakadaira)

https://code.google.com/p/vim/source/detail?r=238f5027830cad22e17a970483af9b160869cdf3

Changes made to original patch:
1. Added type `int` to `i`
2. Changed `mch_memmove` to `memmove`