Git: Support encoding convert of commit messages

Git: Support encoding convert of commit messages

We need read i18n.commitEncoding value, to write correct encoding of the commit file.
In Windows OS, the default encoding is GBK, So we need convert to correct encoding of the commit messages.

Change-Id: Id5f35745dba15da2c9ceb1266e0ea537cba7da73
Merge-request: 382
Reviewed-by: Tobias Hunger <tobias.hunger@nokia.com>