bug#23076: 24.5; vc-git: add a new variable for log output coding system

[Nikolay Kudryavtsev <nikolay.kudryavtsev@gmail.com>]

Eli, sorry for not describing this before in more details, but my data 
in those 3 points was wrong, as I said in the next letter after that one.

So here's how -F flag actually behaves with regards to encodings:
1. When you try to commit using the -F flag with Russian message.txt in 
windows-1251, it gives that warning:
> Warning: commit message did not conform to UTF-8.
> You may want to amend it after fixing the message, or set the config
> variable i18n.commitencoding to the encoding your project uses.

  Then it recodes the log message as windows-1252(sic!). So the russian:
Коммит.
Would become:
Êîììèò.
2. Doing the same while having commitencoding = windows-1251 results in 
a legitimate commit.
3. Having message.txt in utf-8 and commitencoding = windows-1251 results in:
РљРѕРјРјРёС‚.
This is utf-8 recoded to windows-1251.


> My conclusion from these experiments is different.  It seems like Git
> simply records the log messages and outputs them without any
> conversions or interpretation, disregarding i18n.commitEncoding.
That's not true. commitencoding has the immediate effect on the log 
encoding. You can see this by setting commitencoding = windows-1251 and 
doing git log for that test repo.

Log output is decoded by commitencoding, but logoutputencoding overrides 
it. You can test this by:
commitencoding = windows-1251
logoutputencoding = utf-8
This would make git log work again for that repo.

-- 
Best Regards,
Nikolay Kudryavtsev