git-gui: preserve commit messages in utf-8
git-gui: preserve commit messages in utf-8

The commit message buffer is automatically preserved to a local file
but this uses the system encoding which may fail to properly encode
unicode text. Forcing this file to use utf-8 preserves the message
correctly.

Reported-by: Ángel José Riesgo <faa8d0772d761e8d481221613a97d8fd41b49f36@gmail.com>
Signed-off-by: Pat Thoyts <fe43a83262eef1680511f524a1e74d43c633cffe@users.sourceforge.net>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git