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
Moved mch_get_pid and renamed it to os_get_pid
Moved mch_get_host_name and renamed it to os_get_hostanme
Implement os_microdelay and os_delay on top of it
Remove `RealWaitForChar` and `mch_new_shellsize`

The last occurrence of `RealWaitForChar` was replaced by the `os_microdelay`
function. `mch_new_shellsize` had an empty body, so there seems to be no reason
for keeping it around
Add comments and fix `os_microdelay` call