[RFC] Merging vim-patch:7.4.171

Merging vim-patch:7.4.171

Problem:    Redo does not set v:count and v:count1.
Solution:   Use a separate buffer for redo, so that we can set the counts when
                   performing redo.

https://code.google.com/p/vim/source/detail?r=beb037a6c2708f539d50840637f70eed0811d93c